Voice and data transmission over twisted wire pairs

ABSTRACT

A system that provides video signal communication between a source of the video signal and a plurality of units that include destinations of the video signal includes an interface coupled to the source and to telephone lines, each of which serves at least one of the units and carries voice signals to and from one or more telephones coupled to the telephone line at said unit. The interface receives the video signal from the source, and transmits the received video signal onto at least one of the telephone lines in a selected frequency range that is different from frequencies at which the voice signals are carried on that telephone line. This causes the video signal to be coupled to a receiver which is connected to the telephone line at the unit served by that line and is adapted to recover the video signal from the telephone line and apply it to one or more of the destinations at the unit. The source is a cable (e.g., electrical or fiber optic) that is linked to the interface and that carries a plurality of video signals. The destinations are, e.g., televisions. The units can be residences (such as individual houses or apartments in an apartment building) or offices in an office building.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 08/814,837, filed onMar. 11, 1997, which issued on Dec. 1, 1998 as U.S. Pat. No. 5,844,596,which is a continuation of U.S. Ser. No. 08/673,577, filed on Jul. 1,1996, abandoned, which is a continuation of U.S. Ser. No. 08/545,937,filed on Oct. 20, 1995, abandoned, which is a continuation of08/372,561, filed on Jan. 13, 1995, abandoned, which is a continuationof U.S. Ser. No. 08/245,759, filed on May 18, 1994, abandoned, which isa continuation of U.S. Ser. No. 08/115,930, filed on Aug. 31, 1993,abandoned, which is a continuation of U.S. Ser. No. 07/802,738, filed onDec. 5, 1991, abandoned, which is a continuation-in-part of U.S. Ser.No. 07/688,864, filed on Apr. 19, 1991, abandoned, which is acontinuation of U.S. Ser. No. 07/379,751, filed on Jul. 14, 1989, whichissued on Apr. 23, 1991 U.S. Pat. No. 5,010,399.

INTRODUCTION

The present invention relates to a system for simultaneous two-waycommunication of video signals and other signals between multiplenetworks of telephone wiring whose twisted pairs converge together intoa single bundle, wiring block, or other common point of access, and ahigh capacity communication line located at that point of access. Eachnetwork includes a set of interconnected, active telephone wires (i.e.,a group of wires that create a conductive path for telephonic signals)internal to a house, an apartment unit, or a room in a commercialbuilding. (Such wiring internal to houses, apartment units, or rooms incommercial buildings shall be referred to herein as “local networks.”)In the case of houses, the point of common access can be a telephonepole. In the case of apartment buildings, the point of access can be the“wiring closets” found in those buildings. In the case of commercialbuildings, the point of access can be the electronic PBX, or “privatebranch exchange” common to those types of buildings. The high capacityline can be a coaxial cable or an optical fiber. In addition tocommunication between each network and the high capacity line,communication from one network to another is also provided.

This invention is partly an outgrowth of technology presented in theparent application, which issued as U.S. Pat. No. 5,010,399 on Apr. 23,1991, and two other continuations-in-part thereof, respectively entitled“RF Broadcast System Utilizing Internal Telephone Lines” which issued asU.S. Pat. No. 5,929,896 on Jul. 27, 1999 (hereinafter, the “first CIPapplication”) and “Cable TV Distribution and Communication SystemUtilizing Internal Telephone Wiring” which was filed on Apr. 19, 1991 asapplication Ser. No. 07/803,135, (hereinafter, the “second CIPapplication”). The first and second CIP applications were filed on thesame day as this application. The parent application and the first andsecond CIP applications are incorporated herein by reference.

The communication systems disclosed in the parent and first and secondCIP applications are designed to simultaneously transmit telephonesignals and non-telephonic signals (such as cable television signals,other video signals, audio signals, data signals, and control signals)across the active telephone wiring internal to (i.e., locally within)residences and other structures. The present invention adds to thesetechniques, providing distribution of all of these signals to a localnetwork of active telephone wiring (i.e. the wiring internal to a house,apartment unit, or a room in a commercial building) from a distributiondevice that connects to the trunk line of a public or private telephonenetwork. That device is located where the telephone lines for multiplelocal networks converge to meet the public network trunk (or PBX, in thecase of office buildings), enabling the distribution device to performcommunication functions for many local networks at once, includingcommunication between one local network and another. The distributionsystem works just as well when the point of convergence is the center ofa computer communications network with a “star” topology, and the wiresare the twisted pair wires connecting each individual computer to thiscenter.

BACKGROUND OF THE INVENTION

The current method of providing cable TV signals to a house requiresthat a cable branch (typically a coaxial cable) connect from the maincable trunk to each subscriber. In addition, at the end of thesubscriber branch, an additional segment of the coaxial cable must beinstalled for every extra TV “hookup” within the residence.

The challenge of providing cable TV to an apartment building is evenmore formidable. If coaxial cabling is not included at the time ofconstruction, a coaxial cable leading through the entire building mustbe installed, and a branch must connect between each of the individualapartment units to a point on this cable. This is obviously an expensiveprocedure, even if easily accessible cabling conduits exist.Furthermore, each branch provides service at only one location withinthe unit it connects. Extra branches must be installed to provide cableTV service at other locations in the unit.

Providing a group of TV signals to various rooms in an office buildingcurrently requires a similar amount of coaxial cable installation. Thedemand for economical video distribution within office buildings isincreasing, moreover, because of the increased popularity of videoteleconferencing.

The method of distributing cable TV signals commonly used in the U.S.can be called a “one-way branched” system because signals transmitted atthe head-end (i.e., at the root or entrance point to the network) spreadacross to each of the various subscribers by continually splitting intomultiple downstream branches. Due to an increase in the popularity ofvideo programming, however, demand for a new system has emerged. Underthe new system, sometimes called “video on demand,” a subscriber canrequest a specific program from a library of programs stored at acentral location on, for example, video tapes. The signal from thisprogram is subsequently sent to the subscriber from the “head end” ofthe system. No other viewers can receive the same signal unless theymake a similar request.

One method for providing video on demand is to install a high-capacityfiber optic transmission line from the library through a series ofresidential or commercial neighborhoods. At each neighborhood, allsignals targeted for the local residences or businesses (hereinafter,the term “residence” is used to mean both types of buildings unlessotherwise stated) are encoded (i.e. scrambled) and then “handed off” atdifferent channels onto the coaxial cable branch that feeds thoseresidences. Thus, each neighborhood has its own individual headend atthe point of handoff.

To prevent all residences from receiving each of the signals handed offto their neighborhood, a control signal is sent over the fiber optictransmission line that includes the “address” of a converter box in thehouse of the subscriber who requests a particular signal. This controlsignal provides descrambling instructions that, because of theaddressing, only the targeted converter box will recognize. Under thissystem, each subscriber receives all signals targeted for his or herneighborhood, but only the program (i.e., the specific video signal)actually requested by a subscriber becomes available to him or her inunscrambled form.

The concept of “video on demand” can be considered to be part of abroader communication concept. The broader concept is the widening ofcommunication paths to the ordinary subscribers on the switched publiccommunication network. This would enable subscribers to communicatevideo signals and other relatively wide bandwidth signals in the sameway that they currently communicate voice signals.

The transmission medium that is best suited to provide widercommunication paths is fiber optic cables. Indeed, many of the publictelephone companies have converted most of their main communicationtrunks to fiber optics, and have upgraded their switching equipment tohandle these signals and their attendant increase in data rates.

To bring the wider capacity to an individual site, however, requires oneto install a new fiber optic branch from the main fiber optic trunk toeach local network (i.e. a house, apartment unit, or a room in an officebuilding), and to switch signals from the trunk onto the branches.Furthermore, conversion from light to electrical signals must take placeat the point where the branch reaches the targeted residence.(Conversion is necessary because the communication devices currentlyfound in typical residences and offices respond to electrical signals.)Finally, the electrical signals must be distributed through the house.

SUMMARY OF THE INVENTION

The invention described in the second CIP application eliminates theneed for installation of multiple coaxial cable branches within aresidence. Once a feed from the main cable trunk is brought to a houseor apartment unit, the technology described in that application cantransmit signals from that feed onto the internal active telephonewiring of the residence, using those wires to carry the signals to theindividual televisions. Thus, only the coaxial cable which leads fromthe main cable trunk to the residence is necessary.

One general concept that this invention provides is the use of activetelephone wiring (i.e., wiring that is also used for its normal purposeto carry telephone signals) as the transmission line leading from a maincable trunk (which is coaxial cable or fiber optics) to the individualsubscribers. This significantly reduces the complexity and expensenormally associated with cable TV wiring, above the reduction describedin the second CIP application. A major advantage of this wiring overcoaxial cable is that nearly every residence (such as an individualhouse or an apartment unit in an apartment building) has one or morephone lines, each including at least one twisted pair (e.g., thered-green pair; typically, a second twisted pair of black-yellow wiresis also provided) leading to it from the telephone company trunk line. Asecond advantage is that signals applied to the telephone line areavailable at every telephone jack, rather than at a single coaxialoutlet.

Thus, a general aspect of this invention is a system that provides videosignal communication between a source of the video signal and aplurality of units that include destinations of the video signal andthat includes an interface coupled to the source and to telephone lines,each of which serves at least one of the units and carries voice signalsto and from one or more telephones coupled to the telephone line at saidunit. The interface receives the video signal from the source, andtransmits the received video signal onto at least one of the telephonelines in a selected frequency range that is different from frequenciesat which the voice signals are carried on that telephone line. Thiscauses the video signal to be coupled to a receiver which is connectedto the telephone line at the unit served by that line and is adapted torecover the video signal from the telephone line and apply it to one ormore of the destinations at the unit.

Preferred embodiments include the following features.

The source is a cable (e.g., electrical or fibre optic) that is linkedto the interface and that carries a plurality of video signals. Thedestinations are, e.g., televisions. The units can be residences (suchas individual houses or apartments in an apartment building) or officesin an office building. Hereinafter, the term “residence” will be usedfor all such units.

The interface is adapted to select one or more of the video signals inresponse to control information from a user or users of televisions atany residence and transmit the selected video signal or signals onto thetelephone line that serves that residence for recovery and applicationto one or more televisions in the residence. If multiple video signalsare selected for a given residence, the interface transmit the videosignals onto the telephone line that serves that residence at differentfrequencies within the selected frequency range. This prevents theselected video signals from interfering with each other.

The interface can select the same video signal for multiple residencesand transmit the video signal onto the plurality of telephone lines thatserve those residences. Further, the same video signal can be sent overthe telephone lines at the same or different frequencies.

At least one of the residences includes an internal telephone link towhich its receiver and at least one telephone is connected. The internaltelephone link is connected to the telephone line that serves thatresidence, either directly or via a local interface. The local interfaceamplifies video signals received over the telephone line and couplesthem onto the internal telephone link. This helps compensate forattenuation that typically occurs during transmission to the localinterface, thereby increasing the quality of the video signals recoveredby the receiver.

At least one of the residences includes a source (e.g., a video camera)that applies a second video signal that applies said second video signalonto the internal telephone link in a second selected frequency rangethat is different from both the frequency range selected by theinterface and the frequencies at which the voice signals are carried onthe telephone link. The local interface amplifies the second videosignal and couples it onto the telephone line that serves the residenceto cause the second video signal to be coupled to the interface. Theinterface, in turn, transmits the second video signal to the source.

The interface is coupled between the telephone lines and correspondingpublic telephone lines (which carry voice signals at voicebandfrequencies) that serve the residences. In one embodiment, the interfacecouples the voice signals between each public telephone line and eachtelephone line at voiceband frequencies, and the selected frequencyrange exceeds the voiceband frequencies.

In another embodiment, the interface converts the voice signals on thepublic telephone lines to a frequency range above voiceband frequenciesbefore coupling the voice signals onto the telephone lines fortransmission to the residences. In this case, at least a portion of theselected frequency range for the video signals includes voicebandfrequencies. The local interfaces at the residences reconvert the voicesignals to voiceband frequencies and change the frequency of the videosignals to a frequency band above voiceband frequencies before couplingthe voice signals and the video signals onto the internal telephonelink.

A possible drawback of using active telephone wiring to transmit videosignals (e.g., cable TV signals) to the residence according to thisaspect of the invention is that the number of signals that can beeffectively transmitted may be more limited. This, however, can besolved because only a very limited number of signals are typicallyuseful at a single time. One recommended solution is to locate thechannel selection device at the point of connection to the maintelephone trunk (also called the “point of convergence” of telephonelines from multiple residences) and send only the selected video signalsto each residence via the telephone line.

This arrangement can actually achieve extra economies if telephone linesfrom several subscribers converge at one point, as they do in apartmentbuildings and sometimes on telephone poles or pedestals. One economythat can result is that the channel selection electronics for severalsubscribers can be embodied in a single device, thereby reducinghardware cost. The second economy is that scrambling of the signals isnot necessary. Signals not paid for by a subscriber will simply not behanded off onto the telephone lines leading to the residence of thatsubscriber.

Ordinarily, piracy would be a problem because it is easier to “tap” anRF signal from a twisted pair, which is unshielded, than from a coaxialcable. Furthermore, a “tap” onto a twisted pair is less obvious than atap onto a cable.

Because the signals are “handed off” from a point of convergence,however, only specifically selected signals emerge from that point, andthere will ordinarily be less than three video signals on any individualwire (as described in more detail below). By protecting that convergencepoint, therefore, fewer signals are available or piracy than in the casewhere coaxial cables reach all he way to the television. Because easy,surreptitious access to the convergence point will not be available whenthe point is on a utility pole or in the basement of an apartmentbuilding, piracy from the twisted pair distribution system of thisinvention is even more difficult.

The general principles and techniques described in the parent and firstand second CIP applications include some of the ingredients useful toenable converging telephone lines to carry video and other signals froma point of convergence to the individual local networks (i.e. houses,apartment units, rooms in office buildings) in addition to carrying thetelephone signals. Problems can arise, however, due to the unusuallylong path length of the wire branch leading between the point ofconvergence and the internal telephone network within a residence. Otherproblems can arise because the wire pairs from neighboring subscribersare often tightly bundled near the point of convergence. This may causea signal from one wire pair to be picked up by a neighboring pair in thebundle, causing interference. Finally, provision must be made forselection of cable TV channels from within each residence. One of theobjects of this invention is to overcome these problems.

Using active telephone wiring as the transmission line for widebandsignals (e.g., cable TV signals) leading from a main telephone trunkline to the individual subscribers can also improve upon communicationsystems other than those used to distribute ordinary cable TV. Oneexample is the “video on demand” system described above. A shortcomingof the typical video on demand system is the coding and decoding (i.e.,scrambling and unscrambling) that must be provided at each end of thetransmission line. Another drawback is that the excess capacity on cabletrunks carrying cable TV signals is typically very limited. If, forexample, a cable TV franchise provides signals up to cable channel 63(which extends between 462 Mhz and 468 Mhz), the “video-on-demand”signals are restricted to the frequencies above that. Using higherfrequencies may be undesirable because the attenuation of the cableincreases with increasing frequency, and most cable converters are notdesigned to extend that high. If the existing cable can transmit signalsup to, for example, 600 Mhz, then only 132 Mhz, or the equivalent oftwenty-two 6 Mhz AM channels, are available above channel 63 at eachneighborhood. In this situation, at most 22 houses per neighborhood canreceive video on demand.

Telephone wiring from a centralized location (such as the point ofconvergence discussed above) can be useful because it can replace thecoaxial cable as the conductor leading from the cable trunk (e.g., thehigh-capacity fiber optic line) to the individual residences. Oneadvantage of telephone wiring is that it provides a dedicated path fromthe point of convergence to each subscriber. This means that signals onthe optic fiber line that are “handed-off” onto an individual wire pairtransmit to only one subscriber. This eliminates the need for scramblingwhich is otherwise necessary when many subscribers receive a signal(such as over a shared coaxial cable TV network) that only a limitedgroup of them pay for.

A disadvantage, mentioned above, is that such a point of convergence atwhich conductors lead to a large number of subscribers is not alwaysnearby. If some of the subscribers are a great distance from theconvergence point, the attenuation of transmission may be too severe toallow reliable communication across the twisted pairs that comprise thetelephone line.

This problem is less severe in the case of the residential units in anapartment building. Because these buildings typically consist of manyunits whose telephone wire pairs usually converge at a nearby point,such as when a “wiring closet” is provided for each floor, theirtelephone lines are particularly good candidates for providing this typeof communication. Usually, there is a point in the basement of suchbuildings where the wiring from all units on all floors converges.

Commercial buildings also include locations where many telephone linesconverge. Often, the individual wires leading to the various rooms ofthe building converge at what is called a “PBX,” or private branchexchange. Such an exchange is provided because considerablecommunication between rooms is required that is not, of course,economically provided by the public telephone exchange.

As mentioned earlier, the popularity of teleconferencing has created ademand for video distribution within an office setting. Often,videoconferencing allows for a group of workers in a building to monitora conference at a remote location. This requires one-way communicationof video. Other forms of video conferencing, however, require two-wayvideo communication. Using telephone wires for these purposes is morecomplicated, of course, because at least two video signals must transmitin opposite directions. One solution, proposed herein, is to use more ofthe frequencies, or spectrum, available on each wire pair. Another is touse a different wire pair in the same bundle leading to each office, ifit is available. Each of these causes special problems, as will bedescribed herein. One of the objects of this invention is to overcomethe problems associated with two-way communication of video across thetelephone wires in an office building.

Because of the considerable communication demand between rooms in anoffice setting, a demand has also arisen for two-way video communicationbetween rooms in the office. A difficulty in using the telephone wiringfor transmission of video across that setting is that the conductivepaths between the various offices are broken by the PBX. In the firstparent application, a technique to provide a high frequency “bridge”between the various wires leading to a PBX was described, thus makingthe various wires appear, at high frequencies, as a single conductivepath. In this application, that technique is expanded upon to provideswitching of video between offices, and simultaneous communication ofmore signals.

In many office buildings, the telephone wiring is not the only networkof twisted pair wiring that extends to each office and converges at acommon point. Over the past several years, common communication networksthat connect personal computers, known as Local Area Networks or LANs,have begun to use twisted pair wiring for their conductive paths. In thetypical configuration, a digital electronic device serves as the “hub”for such a system, and a separate twisted pair wire connects from thiscenter to each of the computer nodes. Transmission of video across thismedium involves the same problems encountered in transmitting across aPBX system. Additionally, extra difficulties are encountered because thesignals that “naturally” transmit across the system, i.e. the digitalcomputer signals, occupy a much wider band than telephone signals. Inthis application, the technique for communication across a PBX isexpanded to provide the same capabilities for wiring networks thatprovide the conductive paths of a computer local area network (LAN).

In addition to video distribution to houses and apartment units andvideo communication within office buildings, there is a fourthcommunication system that can be improved upon by distributing videosignals over multiple pairs of telephone wires. This system is the mainpublic telephone network itself. The copper wires of this network arecurrently being replaced by fiber optics because these lines can carrymuch more information. Increasing the communication capacity to anindividual residence using current technology requires installation of afiber optic cable spanning the entire distance from the “local exchange”to the residence. The improvement described herein is the result ofusing the existing copper wires to communicate video and other signalsover approximately the last 1000 feet of this link, i.e. from the mainoptical fiber trunks to electronic devices in subscriber facilities.This eliminates the need to install a new communication line betweeneach residence and the main trunk. It also eliminates the need to adapteach electronic device in a residence to receive optical signals.

A new development in video communication colors the entire conceptdescribed so far. The new development is the advent of techniques thatdigitize and compress standard commercial video signals (such as NTSC orPAL) in real time, without reducing information content, so that theresultant digital bitstream has a data rate that is slow enough to beexpressed as an analog waveform in a remarkably narrow channel. Thisdevelopment presents the possibility that considerable programming willbe transmitted in this form in the near future.

Accordingly, it is seen that the present invention provides a techniquefor one-way distribution of signals of a general nature that requirebandwidths much wider than the 3 Khz voiceband currently in use. Thesesignals are transmitted to multiple local networks of active telephonewiring, (i.e. the telephone wiring systems of several houses, apartmentunits, or rooms in an office building) from a signal source at alocation where the active telephone wires leading to the residencesconverge. In the typical application this signal source will be a “tap”into high capacity communication link such as a fiber optic transmissionline or a coaxial cable.

The interface provided by the invention includes a transceiver/switchlocated at the point of convergence. This device replaces the existinginterface between the public telephone network (i.e., an ordinarytelephone trunk line) and the telephone lines that lead to theindividual residences. (These telephone lines are referred to below as“extended twisted pairs”.) Typically, the existing interface will be asimple “punch-down” panel that provides electronic connections betweenthe extended pairs and the pairs that are part of the trunk line. Thetransceiver/switch receives multiple signals (such as several channelsof cable TV signals) from the high-capacity communication link such as acoaxial cable or fiber-optic line, and selectively switches these videosignals onto the individual phone lines, together with the phonesignals. Means are provided at each individual network (i.e. theinternal telephone wiring of each residence) to receive and separatethese signals.

In addition, the invention allows each subscriber to control the signalselection by the transceiver/switch in situations in which a large groupof signals on the high capacity communication link is made available forselection by any subscriber. Control (e.g. channel selection) isestablished by sending signals from a local network to thetransceiver/switch over the extended twisted pair telephone lines, e.g.,in the reverse direction from the direction of transmission of theselected video signals. A particularly appropriate application for sucha system is as an alternative method of distributing cable TV service.

The invention also provides two-way communication of signals of ageneral nature with the high capacity transmission line. This allows theuser to transmit wideband (e.g. 5 Mhz) signals of an arbitrary nature(such as video signals and high data rate computer signals) over theextended twisted pairs from the user's residence to thetransceiver/switch, so that the transceiver/switch can add them to thehigh capacity transmission line for communication with, for example, areceiver at the point where signals transmitting in the “forward”direction originate (e.g., the video library discussed above.) Theinvention further provides two-way switched video communication betweenthe local networks (e.g. the rooms) in office buildings and in otherbuildings that have requirements for two-way communication.

Moreover, all of the communication capabilities discussed above can (andpreferably do) use networks of twisted pair wiring that are also usedfor computer communications.

The communication techniques of the present invention can be adapted toprovide the same capabilities when the signal source at the point ofconvergence provides video signals expressed as analog signalsrepresenting compressed digital bitstreams.

It is important to note that this invention provides the video signalcommunication capabilities described above while preserving all of thefeatures of the pre-existing telephone and computer communications.Thus, interference on the telephone lines between ordinary telephonecommunications and the selected video signals is avoided.

As discussed above, the interface includes a transceiver/switch that isconnected to multiple pairs of telephone wiring and is interposedbetween telephone wire pairs from the local telephone exchange (thetrunk line) and the extended telephone wire pairs leading to separatelocal networks of telephone wiring. The transceiver/switch also connectsto a link used for long distance communication of many multiple signals,such as TV signals.

The invention also includes RF transmitters and RF receivers (describedin detail in the parent and first and second CIP applications) that areconnected to the telephone wiring of the local networks and a localnetwork interface device disposed between the local network wiring andthe extended twisted pair wiring that leads to the transceiver/switch.These elements cooperate to provide the following results:

1) The transceiver/switch can select any one of the signals provided bythe high-capacity communication link and transmit it along the extendedwire pair leading to any one of the local networks. At least one videosignal can be sent to every local network at one time.

2) Normal telephone communication on all local networks and between thelocal networks and the public network (trunk) is preserved. Allpre-existing computer communication capabilities are also preserved.

3) A signal transmitted from the point of convergence will be receivedby the local network interface and retransmitted onto the local network,making it available for reception by an RF receiver connected at anypoint on the local network. (In some embodiments, a local networkinterface is not included and signals transmitted at the point ofconvergence transmits directly onto the local network for reception by avideo receiver connected thereto.)

4) Any RF transmitter connected to a local network can transmit a signalto the transceiver/switch by transmitting that signal onto the localnetwork. A signal sent in this manner is received by the local networkinterface and retransmitted onto the extended twisted pair wire. (Insome embodiments, a local network interface is not included and a signalapplied to a local network by an RF transmitter is transmitted directlyto the transceiver/switch without interception and retransmission.) Atleast one video signal from each local network can be transmitted inthis direction at the same time.

5) Any RF video receiver on a local network can detect control signalsfrom infrared transmitters (e.g., hand-held remote control devicestypically used to control the operation of televisions, VCRs, etc.) andtransmit them to the transceiver/switch, allowing the user to controlprogram selection at the transceiver/switch from the location of, e.g.,any television connected to the local network through an RF receiver.

6) In addition to selecting any one of the signals provided by thehigh-capacity communication link for transmission along the extendedwire pair leading to any one of the local networks, thetransceiver/switch can also select any of the video signals receivedfrom one local network for transmission to any other local network.

Other features and advantages of the invention will become apparent fromthe following detailed description, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a is a block diagram showing the placement of thetransceiver/switch and local network interfaces in a system of telephonelines leading to multiple local networks according to one aspect of tothe invention.

FIG. 1b is a block diagram showing the placement of thetransceiver/switch of FIG. 1a between a PBX (“private branch exchange”)and the system of telephone lines leading to different rooms in anoffice building according to another aspect of the invention.

FIG. 2 is a functional block diagram of the transceiver/switch of FIGS.1a and 1 b.

FIGS. 3a-3 c show different spectral distributions of video signals thatare useful in understanding the invention.

FIG. 4 is a block diagram of a processor in the transceiver/switch ofFIG. 2.

FIG. 4a shows additional details of a component of the processor of FIG.4 that serves as an interface to the high capacity communication line.

FIG. 5a shows another component of the processor of FIG. 4 that performsthe distribution of signals to the various local networks.

FIG. 5b shows an alternative embodiment of the component of FIG. 5a thatallows transmission of signals from one local network to a differentlocal network.

FIG. 5c shows another alternative embodiment of the component shown inFIG. 5a.

FIG. 6a shows additional details of still another component of theprocessor of FIG. 4 that performs the reception and disposition ofsignals sent from the various local networks.

FIG. 6b shows an alternative embodiment of the component of FIG. 6a.

FIG. 7 is a block diagram of a control signal processor in thetransceiver/switch of FIG. 2 for processing the signals sent from thelocal networks to control signal selection and other processing at thepoint of convergence.

FIG. 8 is a table that summarizes the signals transmitted across theextended pairs in one of the examples used in the disclosure.

FIGS. 9a and 9 b are block diagrams of embodiments of a signal separatorin the transceiver/switch of FIG. 2, showing the electronics that routesignals onto multiple extended pairs, route signals received from eachextended pair, and process the telephone signals on the extended pairs.

FIG. 10 illustrates one embodiment of a local network interface of FIG.1a.

FIGS. 11a-11 c show additional details of various embodiments ofcomponents of the local network interface of FIG. 10 that process thenon-telephone signals transmitting between the local networks and thetransceiver/switch.

FIG. 12 shows one of the RF processors (described in the second CIPapplication) that performs part of the function of the local networkinterface of FIG. 10.

FIGS. 13a and 13 b show additional details of the components of thelocal network interface of FIG. 10 that processes the telephone signalstransmitting between the local networks and the transceiver/switch.

FIG. 14 shows additional details of a wiring closet booster thatincludes several local network interfaces for boosting the levels ofsignals transmitting in both directions between the transceiver/switchand several of the local networks.

FIG. 15 is a block diagram of a digital video receiver useful with thesystems of FIGS. 1a and 1 b.

FIG. 16 shows another embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A. Overview (FIG. 1a )

Referring to FIG. 1a, the technology described in this application isdesigned to communicate signals between transceiver/switch 400, locatedwhere individual telephone lines from multiple local networks convergefor connection to a main telephone trunk 476′, and groups of RFcommunication devices that are connected to the individual localnetworks 411 a-411 e of telephone wiring. Each of local networks 411a-411 e (collectively “local networks 411”) includes the wiring confinedto a structure such as a house or to an area within a structure such asan apartment unit or a room in an office building. This wiring providesa single conductive path for a single ordinary telephone signal. Thus,in the case of the common four conductor telephone wiring, the red/greenpair constitutes one local network, and the yellow/black pairconstitutes a second local network. (The only special relationshipbetween these local networks is that they bundle more tightly togetherthan wiring serving different areas. Theoretically, this could increasethe crosstalk between the pairs.)

Note that the details of the wiring of local networks 411 d, 411 e arenot shown in FIG. 1a . Those local networks will not be served by thecommunication system described herein. They are included only todemonstrate that not all local networks within a group whose wiresconverge at a particular point need participate in the communicationsystem described herein.

The wiring of each local network further includes a single branch thatstrays far from the structure, ultimately leading to the point ofconvergence where they connect to (or become part of) trunk 476′. Theseare extended pairs 405 a-405 e, (collectively, extended pairs 405.) Theextended pairs 405 from each of local networks 411 may be bundledclosely together near the point of convergence.

When transceiver/switch 400 is installed, extended pairs 405 are brokennear the point of convergence, with transceiver/switch 400 interposingbetween the two ends of each pair. One segment of each pair remainsconnected to trunk 476′. These segments are called twisted pairs 476a-476 e, (collectively, twisted pairs 476.) Thus, twisted pairs 476 andtheir associated extended pairs 405 ordinarily constitute anuninterrupted connection between local networks 411 and local telephoneexchange 475. In the system described herein, transceiver/switch 400interposes between these wires to provide a link between communicationline 402 and local networks 411. As will be described below, one oflocal network interfaces 404 a-404 c may also interpose along this path,in the middle of or at the opposite end of the corresponding one ofextended pairs 405.

Communication line 402 provides high capacity communication (such as forcable TV signals) with remote locations. Line 402 includes one or morecoaxial cables, optical fibers, or the like. Transceiver/switch 400connects to line 402 to receive and transmit signals. It processes thesignals it receives, and switches them onto selected ones of extendedwire pairs 405 leading to local networks 411, together with (and withoutinterfering with) the telephone signals (e.g., voice signals) that alsouse those wires. The switched signals are received by the RFcommunication devices connected to local networks 411.

Transceiver/switch 400 also receives video, digital, control, and othertypes of signals from extended pairs 405. These signals, which normallyoriginate in the areas served by the local networks 411, are applied tolocal networks 411 by the connected RF communication devices, andtransmit across extended pairs 405 to transceiver/switch 400.

Local network interfaces 404 a-404 c (collectively, interfaces 404) arerespectively interposed on extended pairs 405 a-405 c, thus connectingbetween transceiver/switch 400 and the corresponding local networks 411.Typically, they will be located at a part of extended pairs 405 that iscloser to the corresponding local network 411, rather thantransceiver/switch 400. They assist in the transmission of signals inboth directions between transceiver/switch 400 and local networks 411,as described in more detail below.

Each local network interface 404 intercepts signals sent from thecorresponding extended pair 405, applies amplification and/or othersignal processing, and feeds the resulting signal onto the correspondingone of local networks 411. This assists in the transmission betweentransceiver/switch 400 and local networks 411. Each local networkinterface 404 also performs a similar function to assist signals thatare transmitted in the other direction, i.e., by receiving signals fromone of local networks 411 for transmission to transceiver/switch 400 viaone of extended pairs 405.

As is emphasized at several points in this document, local networkinterfaces 404 need not be used in some conditions, particularly whenextended pairs 405 are relatively short, e.g., less than 300 feet inlength. Such is often the case in apartment buildings. This isfortuitous because there is often no opportunity to interpose a devicebetween the point of convergence and the telephone jacks in an apartmentunit when a transceiver/switch is located in the wiring closet on eachfloor of the building. (When the point of convergence is a room in thebasement where all the twisted pairs converge, the wiring closets aregood locations for local network interfaces, as is described in greaterdetail below. A communication system is shown in FIG. 1b and describedlater on that does not include local interfaces 404.)

The communication devices connected to local networks 411 are nowdescribed. Video receivers 419 a-419 c and 419 a′, video transmitters417 b-417 c, digital transceiver 491 c, and telephone devices 414 a-414c (collectively, telephone devices 414) all connect to local networks411 a-411 c as shown in FIG. 1a. Except for telephone devices 414, allof these devices communicate RF signals over local networks 411, and arereferred to herein as RF transmitters and RF receivers. The RF signalsthey apply to local networks 411 are received by local networkinterfaces 404 and retransmitted across extended pairs 405. (Thesesignals can also be received by other devices connected to localnetworks 411.) Any number of RF transmitters and receivers and telephonedevices can connect to any one of local networks 411.

Each of telephone devices 414 connects via a low-pass filter (LPF). Asdescribed in the first CIP application, these filters prevent telephonedevices 414 from affecting RF energy on the local networks 411. Thesefilters may be provided as part of splitter 161, which is described inthe first CIP application.

The video transmitters and receivers are those described in the parentapplication and in the first and second CIP applications. Videoreceivers 419 a-419 c and 419 a′ (collectively, video receivers 419)connect to televisions 492 a-492 c and VCR 498 a, respectively. Videoreceivers 419 also detect infrared (IR) light signals, convert them toequivalent electrical signals and apply them to the corresponding one oflocal networks 411. These signals transmit across extended pairs 405 totransceiver/switch 400 for purposes described in detail below. Infraredtransmitters 493 a-493 c (collectively, infrared transmitters 493), arerespectively provided at local networks 411 a-411 c to produce the IRsignals.

Video transmitter 417 b connects to video camera 494 b. It derives avideo signal from that device, processes the signal, and applies it tonetwork 411 b. Camera 494 c connects to video transmitter 417 c whichconnects to local network 411 c and operates in a similar manner.Transmitters 417 b and 417 c also receive the control signals applied totheir associated local network 411. They convert these signals toinfrared signals equivalent to the original signal, then broadcast themout into the vicinity for reception by nearby infrared responsivedevices.

Digital transceiver 491 c connects between a computer 495 c and localnetwork 411 c. It receives digital signals from the network wiring andtransmits them to computer 495 c, and it also receives signals fromcomputer 495 c and applies them to the wiring. Digital transmitters andreceivers are described in the first CIP application. That applicationalso describes how to combine RF transmitters and receivers into asingle device that communicates through a single connection to activetelephone wiring.

Except for control signals meant to communicate with transceiver/switch400, the non-telephone signals received from extended pairs 405 bytransceiver/switch 400 are fed to line 402 for transmission to othercommunication devices that connect to line 402 at locations removed fromtransceiver/switch 400. One application for this is to establish asimple two-way videoconference between two people located near oppositeends of communication line 402 or at two points of line 402 that are farfrom each other.

In the reverse direction, transceiver/switch 400 can transmit any of thesignals (such as cable TV signals) selected and recovered fromcommunication line 402 over any one of the extended pairs 405, withoutdisturbing the telephone signals that also use those wires. A singleselected signal (e.g. an ordinary NTSC television signal) can beassigned to more than one pair, and several signals can be assigned tothe same pair.

The processing performed by transceiver/switch 400 on the signals itrecovers from communication line 402 converts those signals to thewaveform (e.g. the modulation type such as AM or FM) energy level, andfrequency band at which they will be effectively transmitted onto wirepairs 405. These signal characteristics must be such that the signalswill communicate with high fidelity over extended pairs 405 a-405 c tothe RF communication devices connected to local networks 411 a-411 c.The relationship between these signal characteristics and the success ofthis communication is discussed at length below.

The selection of the signals from line 402 and their assignment toparticular ones of extended pairs 405 a-405 c (and thus their assignmentto the various local networks 411 a-411 c) is made by transceiver/switch400 in response to the control signals sent from local networks 411 overextended pairs 405. Transceiver/switch 400 also receives and responds tocontrol signals from communication line 402, which can give theoriginator of those signals partial control over signal distribution tolocal networks 411.

The signals from local networks 411 to which transceiver/switch 400responds in making selections are known as “control” signals and aresent by subscribers using infrared transmitters 493. Using techniquespartly described in the parent and first and second CIP applications,video receivers 419 detect these infrared signals, convert them toelectrical signals and apply them to local networks 411. These signalsthen transmit to transceiver/switch 400, as is described below. Controlsignals from local networks 411 can also be generated by other means,and applied to local networks 411 by other RF communication devices. Thedigital transmitters described in the first CIP application, forexample, can respond to manual inputs to transmit an electricalsignal(representing binary information) onto local networks 411. Thiselectrical signal can be used to communicate a channel selection totransceiver/switch 400.

Following is an example of how this system is used to communicate videoand control signals. First, assume communication line 402 conveys 30video signals from a local cable TV franchise. According to theinvention, transceiver/switch 400 selects one or more (typically one ortwo) video signals from among those 30 to be sent to, for example, localnetwork 411 a. Transceiver/switch 400 transmits the selected videosignals over extended pair 405 a to local network interface 404 a.Interface 404 a receives these signals and retransmit them onto localnetwork 411 a, where they will transmit to video receivers 419 a and 419a′ and be provided to TV 492 a and VCR 498 a. Other RF receivers thatconnect to local network 411 a can also receive these signals.

Viewers of television 492 a connected to local network 411 a via videoreceiver 419 a, meanwhile, can use transmitter 493 a to issue infraredcontrol signals to determine which signals are selected and transmittedto local network 411 a. Video receiver 419 a detects these infraredpatterns, converts them to electrical signals, and applies them to localnetwork 411 a. These electrical signals are received by local networkinterface 404 a which processes them and relays the signal acrossextended pair 405 a to transceiver/switch 400. These signals indicate tomaster controller 415 (FIG. 2) the identity of the cable TV signals thatare to be sent to local network 411 a. Alternatively, signals fromcommunication line 402 detected by master controller 415 can alsodetermine the identity of the cable signal to be sent to local network411 a.

The viewer can also transmit video signals from a local network 411 tocommunication line 402. This can be useful for any number of purposes,the most simple of which is to add pictures to an ordinary two-waytelephone conversation. An example of this is where the signal fromvideo camera 494 b is applied to local network 411 b by videotransmitter 417 b. That signal will transmit over local network 411 b tolocal network interface 404 b. Local network interface 404 b receivesthe video signal and transmits it across extended pair 405 b totransceiver/switch 400 which will apply the signal to communication line402. (Again, local network interface 404 b will facilitate thiscommunication only if it is included in the system.) There can be alarge variation in the lengths of extended pairs 405. In an apartmentbuilding, the telephone wires serving different units may converge at apoint 100 feet or less from each apartment unit. An example of the otherextreme occurs when distributing signals to separate houses in aneighborhood. In this case, connecting ten houses to the a singletransceiver/switch 400 may mean that some of extended pairs 405 will belonger than, perhaps, 1000 feet.

Unfortunately, attenuation of the video signals increases withfrequency, which means that the highest useful frequency on extendedpairs 405 decreases with length, ultimately restricting the signals tobelow 4 Mhz. This is a problem because 4 Mhz of bandwidth is theapproximate minimum required for transmission of an NTSC video signal inanalog form. The inventors estimate that this point occurs before thelengths of extended pairs 405 reach 3000 feet.

The solutions described herein take advantage of the improved ability ofRF (radio frequency) signals to transmit over longer distances at lowerfrequencies to avoid problems due to the lengths of extended pairs 405.The invention also takes advantage of the property of conducted RFtransmission that dictates that the tendency for energy from a signal onone wire pair to cross over to a neighboring pair decreases as thefrequency of the signal decreases. This crossover, which can causeinterference, is likely to result when pairs 405 are closely bundledwithin a common sheath, as often happens. Finally, the ability offrequency modulated (FM) signals to resist interference to a greaterdegree than amplitude modulated (AM) signals with more narrow bandwidthsalso plays a part in the system design.

The next part of the disclosure describes the signal flow between majorcomponents internal to transceiver/switch 400, and the processingperformed by those components. That section is entitled “Signal Flow andSignal Processing in Transceiver/Switch 400.” One of the major goals ofthis processing is to convert signals from the form provided bycommunication line 402 to the waveform, frequency band, and amplitudeuseful for successful communication across one of the extended pairs 405a-405 c. The requirements for these characteristics are described in thesection entitled “Transmission of Wideband Signals Over an ExtendedPair.”Two other sections following are entitled “Signal Conversion andSwitching in Transmitter/Switch 400” and “Transmission and Recovery ofSignals from a Single Twisted Pair in a Bundle.” Details of majorprocessing components of transceiver/switch 400 are provided therein.Finally, details of signal processing with in local network interfaces404 is described in the last section, which is entitled “SignalProcessing at the Local Network Interface.

B. “Signal Flow and Signal Processing in Transceiver/Switch 400 (FIG. 2)

Following is a description of a general embodiment of transceiver/switch400. Referring to FIG. 2, the major processing elements oftransceiver/switch 400 are processor 418, signal separators 413 a-413 cmaster controller 415, low pass filters 474 a-474 c, and control signalprocessor 420. Processor 418 serves as the interface to communicationline 402, and each signal separator 413 a-413 c (collectively, signalseparators 413) serves as the interface to the corresponding one ofextended pairs 405. One of the functions of processor 418 is to select,under the direction of master controller 415, video and other signalsfrom communication line 402, to process those signals, and to feed themto signal separators 413. Another function of processor 418 is toreceive video and other signals from signal separators 413, convertthose signals to a form appropriate for transmission on line 402, andfeed them to communication line 402. A third function is to receivesignals from any given one of signal separators 413, convert thosesignals, and to feed them to a different one of signal separators 413,thus establishing communication from one of local networks 411 toanother.

Each of signal separators 413 is connected between one of extended pairs405 and the corresponding one of twisted pairs 476. One of the two majorfunctions of each of signal separators 413 is to transmit signals fromprocessor 418 onto one of extended pairs 405. These signals are appliedso that they transmit onto extended pairs 405 in the direction of localnetworks 411. A second purpose of each of signal separators 413 is torecover signals transmitting from one of local networks 411 over thecorresponding one of extended pairs 405, and to provide these signals toprocessor 418. In some embodiments, signal separators 413 also converttelephone signals so that they transmit over extended pairs 405 atfrequencies above voiceband.

Each of twisted pairs 476 connects to the “exchange” port of thecorresponding one of signal separators 413. In FIG. 2, the “exchange”port is on the left side of signal separators 413, and the “local” portis on the right side. Signals provided by processor 418 to signalseparators 413 transmit out the “local” port onto one of extended pairs405 towards the associated one of local networks 411. Signalstransmitting from local networks 411 to transceiver/switch 400 flow inthe opposite direction. The various ports of signal separators 413 areshown in more detail in FIG. 9a. The details of signal routing withinsignal separators 413 are described below.

In contrast to the “local” port, only telephone signals flow through the“exchange” ports of signal separators 413. Telephone signals transmitover twisted pairs 476 in both directions, transmitting between localexchange 475 and the “exchange” ports, thus passing through low-passfilters 474 a-474 c (collectively, low pass filters 474) duringtransmission.

Low-pass filters 474 connect in series on twisted pairs 476 to suppressthe higher harmonics of telephone signals transmitting across them. Thissuppression prevents the higher harmonics of the telephone signals fromlocal exchange 475 from reaching extended pairs 405, where they couldpossibly interfere with RF signals.

Signal flow between signal separators 413 and processor 418 is nowdescribed. There are two conductive paths connecting processor 418 witheach of signal separators 413. Paths 478 a-478 c (collectively, paths478) conduct signals transmitted by processor 418, and paths 479 a-479 c(collectively, paths 479) conduct signals transmitted by the associatedone of signal separators 413.

The electrical signal, i.e. the voltage variations transmitted to eachone of signal separators 413 from processor 418, may include severalindividual signals at different frequencies that are combined togetheronto the associated one of conductive paths 478. In response to commandssent from master controller 415, processor 418 determines thecomposition of each of these combined signals. After transmission to aparticular one of signal separators 413, each combined signal continueson to transmit to the corresponding one of extended pairs 405.

Other than switching and filtering, no processing of the combined signaltakes place after it leaves processor 418 until it reaches one of localnetwork interfaces 404. Thus, the signal processing performed byprocessor 418 on the individual signals it selects and recovers fromcommunication line 402 determines the waveform (e.g., AM or FM),frequency, and amplitude at which these individual signals aretransmitted across pairs 405.

In the reverse direction, signals transmitted by RF transmitting devices417 onto one of local networks 411 transmit to the corresponding one ofsignal separators 413. (Other devices can also transmit RF signals ontoone of local networks 411. An example is any of video receivers 419,which transmit control signals.) The corresponding one of signalseparators 413 recovers these signals and, except for control signalstargeted for master controller 415, feeds them over the associated oneof paths 479 to processor 418. These signals are received by processor418 and applied to communication line 402. They may also be transmittedto any of local networks 411 that are different from the local network411 of origin.

Control signals originated by subscribers are fed to local networks 411within a specific frequency band, and are transmitted to mastercontroller 415, as described below. This provides a method ofcommunication between a subscriber and transceiver/switch 400, allowingthe subscriber to control, among other things, the channels that areselected from communication line 402 for transmission to the localnetwork 411 where the control signal originated. In a preferredembodiment, these signals are issued by an IR device 493 as infraredpatterns which are detected by video receivers 419, converted toelectrical signals, and fed onto the wiring. Other systems of feedingsignals onto local network 411 within the particular frequency band canalso suffice.

The control signals targeted for master controller 415 are received fromlocal networks 411 by local network interfaces 404 which process themand apply them to extended pairs 405. These signals are recovered frompairs 405 by signal separators 413 and fed over the associated one ofpaths 477 a-477 c (collectively, paths 477) to control signal processor420. Processor 420 processes these control signals and communicates themover path 420 a to master controller 415.

Master controller 415 also receives (via control signal processor 420)control signals that processor 418 recovers from communication line 402and sends over path 420 b. In response to these signals and to thecontrol signals it receives from local networks 411, master controller415 sends signals to processor 418 over links 446 a-446 e (collectively,links 446). Processor 418 determines the selection of signals fromcommunication line 402 and the composition of the signals fed overextended pairs 405 to local networks 411 in response to signals fromlinks 446.

C. Transmission of Wideband Signals over an Extended Pair

As described above, processor 418 selects signals from communicationline 402 and converts them to the waveform, frequency, and energy levelat which they are fed to extended pairs 405. These characteristicsdetermine, to a large extent, the ability of video receivers 419connected to local networks 411 to detect these signals and the abilityof extended pairs 405 to conduct more than one signal at a time.

The nature of the communication medium that is the subject of thisapplication presents two particular problems. One problem is that thereis a significant possibility of crosstalk interference between thevarious signals on extended pairs 405. This possibility is high becausetelephone wires converging at a common point may run parallel and veryclose to each other for a long distance. This makes interferenceresulting from crossover of RF energy between the pairs likely. A secondproblem is that the usefulness of the system is related to the length ofthe longest path over which communication can succeed. This is a problembecause communication bandwidth decreases as the length of a twistedpair communication line increases. (The issue of transmission lengthwill be less important for communication within apartment houses andoffice buildings than they will be for communication with separateresidential structures in a neighborhood. This is mostly because thewires of many different networks in an apartment or office buildingoften converge at a point less than 500 feet from those networks.)

In addition to these problems, there are also particular advantages tothis medium. In particular, because extended pairs 405 connect directlybetween transceiver/switch 400 and local network interfaces 404, thesewires encounter no splits and no connected telephone devices. Thus,signal splitting does not cause problems on extended pairs 405, andconnected telephone devices will also not have an influence ontransmission over those pairs.

The parent and first and second CIP applications describe many of therelationships between the properties of a signal and its tendency to beattenuated and distorted during transmission across telephone wiring. Asdescribed therein, the maximum transmission length increases withdecreasing frequency because of improvements in transmissioncharacteristics. Specifically, attenuation, radiation, and the abilityof the wiring to pick up (interfering) broadcast energy all decrease astransmission frequency is reduced. Also, crossover of energy betweenneighboring pairs decreases with decreasing frequency. Thoseapplications also discuss spectral tilt, another undesirable byproductof transmission over telephone lines.

The first CIP application explains that FM video signals have a greaternoise immunity than do AM video signals, i.e., the SNR afterdemodulation of an FM signal is higher than that of AM video signals ifthe frequency modulation process creates a signal with a wider bandwidththan the AM signal. As explained in the first CIP application, thesensitivity advantage of FM video signals over AM increases as thebandwidth of the FM signal increases.

The ability of FM signals to reject interference increases when theinterfering signal is a second FM signal confined within the samechannel. As explained in the first CIP application, the minimum energyadvantage that a receiver requires to reject a weaker but otherwiseequivalent signal in the same channel is known as the “capture ratio”,and is often significantly less than the minimum SNR necessary to avoiddistortion by white noise. The exact capture ratio will depend onseveral factors, but the inventors estimate that the “capture ratio” ofan FM NTSC video signal with a 15 Mhz wide bandwidth will typically beless than 10 dB, allowing it to ignore interfering FM signals whoselevels are suppressed by at least 10 dB.

Using FM to transmit video has three disadvantages, however. One is thatthe tuning circuitry of common television sets expects to receive AMsignals. This means that an extra signal conversion may be requiredbefore a picture is generated. Secondly, FM video electronic circuitryis more expensive. The third disadvantage is that a group of adjacent FMvideo channels will cover a wider band than a group of adjacent AMchannels. In addition to occupying more spectral area, a band ofadjacent FM channels will reach higher frequencies than a band of thesame number of adjacent AM channels (assuming that both bands begin atthe same frequency). Signals transmitting over FM channels, therefore,will generally suffer more from the problems associated with increasingfrequency.

When processor 418 transmits several signals simultaneously across oneof extended pairs 405, it assigns each signal to a separate frequencyband, or channel. The energy of each signal will be confined within thatband. (Effectively, this “channelizes” that particular extended pair405.) Additionally, processor 418 determines the waveform and energylevel of each individual signal. On the basis of the considerationsdescribed above, a set of guidelines have been developed to aid indetermining these characteristics for a given communication scenario.Some of the guidelines apply to transmission of signals of a generalnature. Other guidelines will apply only to television signals. Stillothers will apply only to the specific situation of the communication ofone or two video signals over especially long distances. Theseguidelines are disclosed in the following paragraphs (1-6).

1) Energy Level

Because RF signals that may be transmitted across telephone lines arerelatively low in power, increasing signal level is not likely to causea significant increase in cost, and is also not likely to cause problemsof safety. Furthermore, maximizing the signal levels maximizes the SNRat the receiver. Thus, there are no benefits to lower signal levels, andthe signal level should be set so that the resulting radiation fallsjust below governmental limits on the airborne radiation.

Because telephone wiring is unshielded, EMF radiation will result nomatter how well the transmitting or receiving devices are shielded.Thus, these radiation levels will not significantly vary with any factorother than the signal level. This means that the radiation can bedetermined at the time of manufacture, avoiding the expense of providingfor adjustable signal levels.

For example, following FCC procedures, the inventors fed a 22.45 MhzNTSC video signal onto a telephone wire and measured the resultingradiation. It was found that at a conducted signal level ofapproximately 50 dB mV, radiation from the wire would be just below thegovernmental limits of 30 uV/M measured at 30 Meters. Thus, a level of50 dB mV would be preferred for a transmitter that applies a 22.45 Mhzvideo signal to telephone wiring.

2) Adjacent Low-Frequency Channels

As described above, attenuation, radiation, crosstalk interference andreception of external interference all increase as frequency increases.This means that the signal with the highest frequency is most likely tohave the lower SNR, and that overall communication success can beimproved by lowering the frequency below which all signals are confined.

To minimize the highest frequency used for transmission, it isrecommended that the first channel be placed as close to the voicebandas feasible, and that each succeeding channel be placed above andadjacent to the previous channel. The channels should be separated infrequency sufficiently, however, to allow clean separation at thereceive end without excessive filtering costs.

3) Minimum Frequency

If AM is used to transmit video signals, it is preferred that thepicture carrier of the first such channel be located above 4.25 Mhz.This frequency is chosen as a rough compromise between the followingfactors: a) transmission properties improve with lower frequencies; b)as described in the first CIP application, the likelihood of distortionof AM signals caused by the phenomena of spectral tilt increases withdecreasing picture carrier frequency below 5 Mhz; and c) there arecertain advantages in arranging for transmission of several adjacent 6Mhz AM NTSC video signals beginning with a signal whose picture carrieris at 4.45 Mhz. (One major advantage, which is described more fully inthe second CIP application, is that arranging video channels in thismanner reduces the likelihood of interference from amateur radios.) ForFM transmission, it is preferred that the low end of the first channelbe 4 Mhz. This frequency is chosen as a rough compromise between thefollowing considerations:

a) Transmission properties improve at lower frequencies;

b) Spectral tilt becomes more pronounced with increasing ratios betweenthe highest and lowest frequencies of an FM signal. (the problem of thespectral tilt of FM signals is described in the first CIP application);

c) lowering the low end of an FM band by 1 Mhz does not provide asignificant decrease in the percentage reduction of the frequency of thehigh end. For example, moving the low end of a 15 Mhz channel from 3 Mhzto 2 Mhz only reduces the upper frequency by 5%, i.e. from 18 to 17 Mhz.

4) Bandwidth

Assume that “N” different signals are to be transmitted within adjacentchannels, that the average width of the channel confining a signal is BMhz, and that the low end of the lowest channel is k Mhz. Under theseconditions, the high end of the channel highest in frequency is given by(Nb+k) Mhz. Thus, decreasing bandwidth decreases the maximum frequency.

Because of this, a preferred system when transmitting multiple NTSCvideo signals is to provide all signals using AM modulation within 6 Mhzchannels distributed according to the NTSC standard. (I.e. a picturecarrier 1.25 Mhz above the low end and a sound carrier 0.25 Mhz belowthe high end.) This arrangement is chosen because the bandwidth isrelatively narrow, yet separation can be achieved using inexpensivefiltering. This is the same arrangement that was chosen for airwavetransmission of video shortly after the invention of television. Thesame justifications applied. Because of that standard, very inexpensiveelectronics exist for this type of channeling, providing anotheradvantage.

The preferred lower end for the band of transmission over extended pairs405 is defined by an AM signal with a picture carrier of 4.45 Mhz. (Thelower end of an NTSC video channel with a carrier of 4.45 is at 3.2 Mhz.This is because the bottom of the 6 Mhz channel is 1.25 Mhz below thepicture carrier.) The advantages of providing adjacent AM signals withpicture carriers spaced 6 Mhz apart and beginning at 4.45 Mhz aredescribed in the second CIP application. Also, a picture carrier of 4.45Mhz is above the minimum frequency requirement of 4.25 Mhz suggestedabove.

Amplitude modulation is particularly adequate when only a small numberof signals transmit over a short distance. As transmission distanceincreases, attenuation causes the SNR at the receiving end to drop.Similarly, as more channels are added to a wire pair of fixed length,one is forced to use higher frequencies, until the signal at the highestfrequency is not received with an adequate SNR. (Note that capacitytightens up very rapidly with increasing frequencies because attenuationincreases and at the same time the signals radiate more, forcing areduction in the initial signal levels.)

A third phenomenon that can cause an inadequate received SNR is thepresence of broadcast energy, which elevates the noise level. This islargely a function of the radio broadcasters in the area, but it is alsorelated to frequency because telephone wiring acts as a more efficientantenna as the frequency of the broadcast signal increases.

5a) Increasing Bandwidth to Counter Signal Attenuation

When the attenuation of transmission or the presence of broadcast energyat the “unused” frequencies on a transmission line suppresses the SNR atthe receive end below the minimum required for AM video, the proposedsolution is to use frequency modulation with bandwidths significantlylarger than 4 Mhz. (Four Mhz is the approximate bandwidth of an NTSCvideo signal at baseband.) As mentioned in the first CIP application,receivers in FM communication systems that use 15 Mhz of bandwidth perNTSC video signal are known to produce a demodulated signal that isapproximately 10 db higher than the SNR at its input. This is animprovement over AM systems because, in those systems, the SNR at thereceiver output is equal to the SNR at the receiver input.

Following is an example. Assume that nine AM NTSC signals transmitacross a path 400 feet long within adjacent 6 Mhz channels beginning at6-12 Mhz and ending at 54-60 Mhz. Now assume that a signal of 45 dB mVwith a carrier at 61.25 Mhz, (corresponding to the channel between 60-66Mhz), creates radiation just below the legal (FCC) limit when applied totelephone wiring. Because the attenuation on telephone wiring at 60 Mhzis approximately 12 dB per 100 feet, the SNR of such a signal at thereceive end of the above path should, theoretically, be −3 dB mV, or 3dB below the minimum (0 dB mV) required for high quality videoreception.

A solution is to transmit a 15 Mhz wide FM signal between 60 Mhz and 75Mhz. The high end of this signal, being at 75 Mhz rather than 66 Mhz,will suffer greater attenuation, and will also radiate more energy.According to measurements performed by the inventors, however, theradiation difference will be negligible, (perhaps 1 dB), and the extraattenuation at 75 Mhz over the 400 foot path will be approximately 2 dB.Thus, the received level will be approximately −6 dB mV. If the SNR atthe output of a 15 Mhz FM video receiver is approximately 10 dB higherthan the SNR at the input, however, the SNR of the demodulated videosignal will be 4 dB, which is sufficient. Thus, transmission of an extrachannel can be enhanced by using FM for the additional channel.

At higher frequencies, the 10 dB advantage of a 15 Mhz FM signal may notbe sufficient to overcome the extra attenuation. The solution, in thatcase, is to use wider FM bandwidths which produce a greater SNRimprovement at the receiver. This, of course, brings one to even higherfrequencies more quickly with each channel that is added. Because ofthis, the inventors expect that higher frequencies will not be usefulbeyond some point, and certainly not beyond 1000 Mhz.

5b) Using FM to Counter Crosstalk

Within a bundle of unshielded telephone wire pairs, the amount of energyradiated by one pair that is received by another increases withfrequency. This happens both because the radiation at a fixed signallevel increases with frequency, and because the ability of the secondwire pair to “pick up” the radiation also increases. This energyreceived by the second wire pair is known as “crosstalk” and thetendency of a particular medium to exhibit this type of interference isknown as “crosstalk loss.” That quantity is the ratio, in dB, betweenthe signal directly applied to a communication line and the energyreceived from the radiation of a signal of equal strength fed to aneighboring line. The greater the “crosstalk loss,” the less theinterference.

At the voiceband frequencies of ordinary telephone signals, which arebelow 5 Khz, crosstalk loss is very high. Thus, the portion of the“noise” typically encountered by telephone signals that is related tocrosstalk energy is very small. For this reason, telephone signals onneighboring wire pairs usually do not interfere with each other.

At frequencies above 1 Mhz, however, interference from crosstalk can besignificant. Crosstalk loss will be affected by many different factors.According to measurements, made by the inventors, of several bundles of12 pair and 25 pair telephone wires, crosstalk loss at 6 Mhzoccasionally becomes less than 45 dB, while crosstalk loss above 50 Mhzrarely exceeds 40 dB. These measurements indicate that AM video signals,which can display the effects of interference at SNRs as low as 40 dB,may suffer interference from crosstalk at even relatively lowfrequencies such as 6 MHz.

FM signals, on the other hand, have impressive resistance to crosstalkinterference because of their very low “capture ratios.” As stated inthe first CIP application, the inventors estimate that receivers thatprocess FM video signals with bandwidths of 15 Mhz or more can rejectinterference from any FM signals transmitting in the same channel if thelevel of the interfering signal is weaker by 10 dB or more. Thus, itwould appear that FM video signals will not encounter crosstalkinterference until at least 50 Mhz, and the use of FM at the very lowestvideo channel may be indicated.

5c) Using Secondary Pairs for Additional Channels

As mentioned above, there is an upper limit to the frequencies that canbe useful for transmission of signals across a transmission path of agiven length. Thus, the number of signals that can transmit over anextended pair to a given local network is limited.

In most apartment buildings, however, several extended pairs service(i.e. are dedicated to) each apartment unit. Each of these pairstypically branches off to connect to each of the jacks in the unit.Typically, one of these pairs conducts the signals for the primarytelephone service to that unit. Additional pairs are left empty unlessand until secondary telephone lines are requested. Thus, apartment unitsare typically serviced by more than one of extended pairs 405 and,correspondingly, more than one of local networks 411.

An example is where red, green, black, and yellow conductors connect ateach jack in a unit and also extend down to the point of concentrationin the basement of the building. The red and green wires in the unitconstitute one of local networks 411, and the yellow and black wiresconstitute a second of local networks 411. The lengths of these wiresthat extend down to the basement of the apartment building constitutethe extended pairs 405.

If more signals are required than can be accommodated by a singleextended pair, the extra wires present an opportunity. As describedearlier, the twisted pairs connecting to the same unit may be bundledmore tightly together than arbitrary pairs in the same bundle,potentially increasing crosstalk interference. If this increase is notdramatic, however, the techniques to avoid crosstalk described abovewill be sufficient to prevent crosstalk interference between signals onthese two pairs that serve the same unit, preserving the opportunity fortransmission of additional signals.

Indeed, using an additional pair for the second channel provides theeconomy that fewer frequency bands are required to transmit a givennumber of signals. For example, assume that transmitting two signals canbe done by using FM within the channels between 6-18 Mhz and 18-30 Mhz,and that at most two signals are required by any unit. It may be moreeconomical, in this case, to provide the second signal within the 6-18Mhz channel but on a secondary pair. This allows video receivers 419 toreceive either signal using only the electronics necessary to tune the6-18 Mhz channel. Switching from one signal to the other is simply amatter of switching between wire pairs.

Transceiver/switch 400 can enjoy a similar economy. Using the exampleabove, transceiver/switch 400 need only be equipped to transmit withinthe 6-18 Mhz channel to satisfy the system requirements.

5d) Transmitting over Unused VHF Channels

As described in the first CIP application, systems that transmit signalsat unused VHF television channels are very reliable because they enjoythe advantage of total immunity (as a practical matter) from broadcastinterference. It was further described how the relatively highattenuation suffered by signals transmitting at those relatively highfrequencies can be overcome, in some circumstances, by using low-passfilters to remove all of the attenuative affects of all telephonedevices connected to the wiring.

Because cable TV companies consider reliability an extremely importantpart of their delivery systems, use of unused VHF channels within thesystems described herein is an interesting option. For example, a cablecompany considering distribution of AM signals through an apartment unitwithin 6 Mhz channels below 30 Mhz may be concerned that an amateurradio enthusiast can erect an antenna nearby and broadcast at the 10meter, 15 meter, 20 meter, and 30 meter bands, all of which are below 30Mhz.

One of the problems of using unused television broadcast channels in thesystems that are the subject of this application, however, is that thewires leading to the various units may be bundled tightly together,causing the crosstalk problems described above. Crosstalk interferenceis even more likely to occur because crosstalk increases with frequency,and unused TV channels are at relatively high frequencies. Also, becauseadjacent unused channels are not typical, only 6 Mhz is available perchannel, preventing the use of FM, which is more resistant to crosstalk.

In many apartment buildings, however, the wires providing telephonesignals to an individual unit are often not bundled tightly togetherwith wires leading to other units. This is especially common for thewires that lead from a “wiring closet” that serves as a concentrationpoint for the various units on the same floor. Often, separate bundlesof four or more conductors lead from this point to each apartment unit.Because the bundles are separate, crosstalk will be negligible. Becausethey need not traverse between floors, moreover, these bundles arerelatively short in length, decreasing the likelihood that they willexceed the relatively short transmission length limits imposed by unusedtelevision channels.

The combination of short path lengths and separate bundles is an idealconfiguration for transmitting over the unused television channels.Following is an example. Assume a five story apartment building in NewYork City includes five units on each floor, and that four wires serviceeach of the units on a floor. Assume further that the conductors fromeach unit are bundled together and lead to a wiring closet on the samefloor. Inside each wiring closet, transceiver/switch 400 is installedand connected to the cable TV trunk which is brought to each closet.(Leading this cable to each closet is the only wire installationrequired.) In New York City, VHF channels 2, 4, and 5 are used, makingVHF channels 3 and 6 open for transmission. Using the technologydescribed herein, transceiver/switch 400 feeds two different signals,one at VHF channel 3 and one at VHF channel 6, onto one of the twistedpairs leading to each unit. Note that the second twisted pair willtypically not be useful because it is bundled too closely to the firstpair.

6) Transmission of Video using Compressed Digital Signals (FIG. 15)

Currently, extensive effort is focused on developing methods to compressdigital representations of NTSC video signals. These efforts havereached the point where it appears that the digital bitstreamrepresenting an NTSC video signal can be compressed sufficiently so thatit can be transmitted within a channel narrower than the 4 Mhz occupiedby the video portion of the original analog NTSC signal. In other words,the digital bitstream can be expressed, using techniques such as pulsecode modulation (PCM), as an analog signal with a bandwidth less than 4Mhz. Furthermore, the SNR required for accurate reception of this signaland recreation of the compressed bitstream is less, potentially, thanthe SNR required for quality reception of FM video signals. Also, thedigital signal has similar resistance to crosstalk interference. Thus,it appears that video signals can be communicated more efficientlyacross networks of the particular type discussed herein if they are indigital form. The drawback of digital transmission of video, of course,is the expense of digitization and compression of the video signal atthe transmit end, and the expense of the inverse processes at thereceive end. Because it is expected that compression circuitry willdramatically decrease in price, techniques to transmit compresseddigital video signals are included in a later section of this disclosureand shown in FIG. 15.

D. Two-Way Transmission of Video Signals

The guidelines for choosing transmission bands and modulation methodsfor transmitting video signals from transceiver/switch 400 to localnetworks 411 also apply for transmission in the opposite direction. Anextra consideration arises, however, when transmission in bothdirections takes place simultaneously. The consideration is a form ofinterference sometimes called “nearend crosstalk.” This interference canoccur when signals are fed to a wire pair at one end while signalstransmitting at the same frequencies are received from a neighboringpair (in the same bundle) at the same end. To see why this type ofsituation is likely to cause interference, consider the followingexample.

Assume that transceiver/switch 400 modulates a first video signal usingAM with a carrier frequency of 8 Mhz and feeds it onto extended pair 405a, and that local network interface 404 b modulates a second videosignal using AM and a carrier at the same frequency and feeds it ontoextended pair 405 b towards transceiver/switch 400. Assume further thatthe attenuation of transmission at 8 Mhz is 2 dB per 100 feet, and thepaths, i.e. pairs 405 a and 405 b, are 1000 feet long.

Now consider the signals present at transceiver/switch 400 on pair 405b. The level of the first signal is simply that produced bytransceiver/switch 400 minus the loss in energy as it leaks from pair405 a onto pair 405 b. The level of the second signal, which is thesignal of interest on 405 b, is 20 dB lower than that produced byinterface 404 b because of the attenuation of transmission. Thus, if thesecond signal is an AM video signal, interference will occur unless thefirst signal loses at least 60 dB crossing from 405 a to 405 b.Experiments performed by the inventors indicate that, in typicalsituations and at frequencies above 5 Mhz, the crossover loss is likelyto be much less than that, perhaps even low enough to cause interferencewith FM video signals.

The solution proposed herein is to ensure that the bands used fortransmission in the “forward” direction, i.e. from transceiver/switch400 to local networks 411, are the same for each of extended pairs 405.In other words, the frequencies used by signals transmitting alongextended pair 405 a from transceiver/switch 400 to local network 411 aare not also used by signals transmitting over extended pair 405 b inthe reverse direction, i.e. from local network 411 b totransceiver/switch 400.

As described above, a very important application of the techniquesdisclosed herein is the one-way distribution of cable TV signals. Inthese types of applications, wideband video signals are transmitted fromtransceiver/switch 400 (i.e.,the point of convergence) to local networks411, and control signals, which will be narrowband because they havevery small information content, transmit in the opposite direction toprovide the selection mechanism.

In these situations, where only a very narrow (e.g. less than 0.5 Mhz)signal transmits towards transceiver/switch 400, it is preferred thatthe narrowband signal transmit just above voiceband, below the widebandsignals. This reduces the expense of filtering, because the cost of afilter is inversely proportional to its “fractional bandwidth,” which isthe bandwidth divided by the center frequency. Thus, a 0.5 Mhz filter at1 Mhz, for example, has a fractional bandwidth of 0.5, and thefractional bandwidth of a 6 Mhz video signal at 4 Mhz is 1.5. Reversingthe frequency order of the narrowband signal and the video signal, i.e.,placing the narrowband signal at 7 Mhz and the video signal at 3 Mhz,makes these fractional bandwidths 0.07 and 2, dramatically decreasingthe fractional bandwidth of the narrowband signal, without significantlychanging that of the video signal.

E. Transmitting a Single Video Signal over Long Transmission Lengths(FIGS. 3A-3C)

When transmission lengths are longer than 1000 feet, transmissionproblems may be encountered even at frequencies below 10 Mhz. In thesetypes of situations, use of extended pairs 405 to communicate multiplesignals over a large frequency range may not be feasible. A system thatcommunicates only a single video signal, however, can still be veryuseful in many important applications.

To provide for communication of a single video signal undercircumstances of long transmission length, three different sets ofspecific waveform/frequency combinations are shown in FIGS. 3a-3 c anddisclosed below. To gain extra transmission length, each of these usesfrequencies below the lower limits suggested above.

Each of these techniques has advantages and disadvantages vis-a-vis theother two. One technique is to transmit the signal amplitude modulatedat a frequency slightly above voiceband (FIG. 3a). A second technique istransmit an unmodulated signal at baseband (FIG. 3b). The thirdtechnique is to transmit the signal frequency modulated within a bandhaving a low end of approximately 3 Mhz (FIG. 3c).

One of the applications where communication of a single video signal canbe important is in transmitting cable TV signals over extended pairs405. In this case, provision is made for the user to select the signalto be transmitted. Methods of encoding low data rate bitstreams, e.g.,100 bits per second, into signals with narrow bandwidths, e.g., lessthan 0.5 Mhz, that can tolerate very low SNR levels at the receiverinput are well known. Thus, it will be appreciated that the “selection”(i.e., control) signal can normally be transmitted at frequencies abovethe video signals in each of the techniques described below, and stilltolerate the added attenuation of those higher frequencies.

Alternatively, in the case of the distributions shown in FIGS. 3a and 3c, there is “room” to transmit a narrow band control signal between thevoiceband and the video signal. Because placing narrowband signals nearthe voiceband reduces filtering costs, as described above, this is apreferred method of transmitting these signals. Thus, FIGS. 3a and 3 callocate a small part of the spectrum between the voiceband and thevideo signal to these selection signals.

The distribution shown in FIG. 3b does not allow this because the videosignal extends down to baseband. In this situation, a preferred methodis to transmit the narrowband “selection signal” in a frequency bandabove both the video information and the telephone signals.

1) Amplitude Modulation within a Low-Frequency Channel (FIG. 3a)

In the first technique, processor 418 converts each video signalselected from communication line 402 to an AM signal whose carrierfrequency is below 3 Mhz, and is preferably closer to 1 Mhz. To preventinterference with telephone signals, the lower sideband of this signal,known as the lower vestigial sideband, is suppressed to substantiallyeliminate the energy in the voiceband.

FIG. 3a shows the spectrum of such a signal. The carrier frequency is1.25 Mhz, with the lower sideband substantially suppressed below 1 Mhz.The 1.25 Mhz frequency is chosen as a compromise between thetransmission advantages of lower frequencies (which are described in theparent and first CIP applications,) the disadvantages of lowerfrequencies (which are described below), and a particular advantage ofthe specific frequency of 1.25 Mhz (described in the next paragraph).

One of the disadvantages of lower frequencies is that the filtering thatseparates these signals from voiceband signals is more expensive becauseof the sharp cutoff required between the upper end of the voiceband and1 Mhz. A second disadvantage is that the harmonics of the telephonesignals at lower frequencies are stronger, meaning that strongerfiltering of the harmonics is required to protect against interferencefrom these signals. A third disadvantage is that the modulationelectronics become more expensive as the picture carrier approaches DC.The particular advantage of the 1.25 Mhz picture carrier is that itcoordinates with one of the channelization schemes disclosed in thesecond CIP application.

In the channelization scheme shown in FIG. 3a, the audio component ofthe television signal is frequency modulated with a carrier frequency of5.75 Mhz. That is, the audio component is placed slightly above thehigh-end of the video band. In particular, it is spaced 4.5 Mhz abovethe video carrier, thus following the convention of standard NTSCchannels.

The signals whose harmonics are likely to cause the interferencedescribed above are those with high energy, such as ringing signals, andsignals relatively high in frequency such as the transient signals thatoccur with sudden voltage changes during hook-switching. Ordinarily, theharmonics as high as radio frequencies are harmless because the energylevel of a harmonic series reduces with frequency. Because of therelatively low frequencies of the video signals, however, theseharmonics may still have significant energy when reaching the samefrequencies.

The ringing and transient signals originate at local exchange 476 orwithin telephone devices 414. To prevent this type of interference,these sources are filtered, preventing the harmonics from transmittingonto extended pairs 405. This filtering is now described.

Referring again to FIG. 2, filters 474, which include low-pass filters474 a-474 e, respectively, placed in series on each of twisted pairs 476a-476 e, block the harmonics of telephone signals that originate atlocal exchange 475 from transmission to extended pairs 405. This avoidsinterference with RF signals transmitting over those wires. Similarly,transients and harmonics created by the telephone devices 414 on localnetworks 411 are blocked from crossing over to extended pairs 405 byfiltering within local network interfaces 404. That filtering is shownin FIGS. 13a-13 b and is described below. In the embodiments where localnetwork interfaces 404 are not provided, other filtering must block theharmonics of telephone devices 414. This filtering is provided by thelow pass filter (LPF) interposed between each of telephone devices 414and the network wiring, as shown in FIG. 1a.

As described in the first CIP application, the video signal shown inFIG. 3a may suffer from the problem of spectral tilt because it isamplitude modulated with a picture carrier substantially below 5 Mhz. Toreduce this tilt, processor 418 pre-emphasizes, or amplifies, the higherfrequencies of the signal by a greater amount than the lowerfrequencies. This pre-emphasis is performed in processor 418 bymodulators 410 a-410 d (collectively, modulators 410) as describedbelow.

If pre-emphasis is not provided, or if the signal arrives at thecorresponding local network interface 404 with a significant tiltdespite precautions, processing in interface 404 can include means knownas equalization that estimate the tilt and adjust the spectrumaccordingly. Alternatively, equalization can be performed in videoreceivers 419 that recover signals from local networks 411 and providethem to televisions 492.

In the reverse direction, compensation for spectral tilt is implementedby providing pre-emphasis in video transmitters 417 or in localinterfaces 404. Alternatively, equalization of the video signalsreceived from extended pairs 405 can be provided in demodulators 416 ofprocessor 418, as described below.

The preferred compensation technique for the spectral tilt of signalstransmitting to local networks 411 is to perform pre-emphasis inprocessor 418. The preferred technique for compensation of signalstransmitting in the opposite direction is to use equalization inprocessor 418. These techniques are preferred because using them wouldconfine all the special compensation circuitry in a single device,transceiver/switch 400, which would seem to be economical. Also,adjustment of the compensation circuitry must normally be done for eachof extended pairs 411. Thus, performing an adjustment for an entiresystem is more convenient when the adjustment controls are confined toone device.

2) Transmitting Unmodulated Video Signals over Active Twisted Pairs(FIG. 3b)

Referring to FIG. 3b, an alternative to transmission using AM at a lowfrequency is to transmit the video signal in its unmodulated form. Thiswill reduce (e.g., by 25%) the highest frequency used by the videosignal below that of the previous example from 5.25 Mhz to 4 Mhz,reducing the attenuation of transmission and providing a furtherincrease in the length over which transmission can succeed. Equallyimportant, crosstalk energy from neighboring pairs will also decrease.

Because the unmodulated video signal occupies voiceband frequencies,telephone signals on extended pairs 405 are transmitted within afrequency band above the unmodulated video signal to preventinterference. As shown in FIGS. 9b and 13 b and described below, signalseparators 413 (FIG. 9) and local network interfaces 404 (FIG. 10)cooperate to ensure that the telephone signals transmit above 4 Mhz onpairs 405. FIG. 3b shows the 0.5 Mhz band centered at 5.0 Mhz allocatedto telephone signals.

Transmission of a television signal also requires, of course,transmission of audio information. As shown in FIG. 3b, the audioinformation transmits FM encoded at 4.5 Mhz, just above the end of thevideo spectrum. This is consistent with the NTSC standard. Controlsignals for channel selection are transmitted within a 0.5 Mhz bandcentered at 5.5 Mhz.

Provision of the telephone, control, and audio signals above the videoband would seem to defeat the advantage of using unmodulated signals toreduce the maximum frequency. Because the information content of theaudio and telephone signals are very low, however, these signals can beFM encoded so that the minimum SNR that they require at the receiver ismuch less than the 40 dB required by an AM video signal. This means thatthe transmission length is limited by the attenuation at the upper bound(4 Mhz, in this case) of the video signal, and that distortion fromcrosstalk interference will be caused by crosstalk at 4 Mhz before it iscaused at the frequencies used by the audio and the telephone signals.

To transmit unmodulated signals, processor 418 receives signals fromcommunication line 402 and demodulates them, if necessary. Processor 418then amplifies these signals, and switches a separate signal on each oneof paths 478 leading to signal separators 413.

Under the proposed scheme, telephone signals from local exchange 475that transmit over twisted pairs 476 at voiceband frequencies areconverted to RF frequencies (FM, with a 5.0 Mhz carrier frequency) bysignal separators 413 and fed onto extended pairs 405. Electronicswithin local network interfaces 404 convert the RF telephone signalsback to baseband and the video signals to an RF frequency, and feed bothonto local networks 411. This allows the telephone signals to bereceived from local networks 411 by telephone devices 414 in theordinary manner. (Because they are at baseband, the telephone signalswill pass through the low pass filter (LPF) connected between each ofdevices 414 and the local network wiring.)

In the opposite direction, telephone signals are fed to local networks411 by telephone devices 414. These are intercepted by local networkinterfaces 404, converted to RF signals, and fed onto pairs 405 towardstransmitter/switch 400. These signals are received by signal separators413, converted to ordinary voiceband telephone signals, and fed (viafilters 474) onto pairs 476 leading to local exchange 475.

Some of the details of the telephone signal processing are shown inFIGS. 9b and 13 b and are described in detail below. Note that localnetwork interfaces 404 are needed to implement this scheme.

Because energy at the frequencies near DC will be attenuated much lessthan energy at 4 Mhz, the spectrum of the video signal is likely to tiltsignificantly during transmission over extended pairs 405. The samepre-emphasis and equalization techniques described to compensate for thetilt of low-frequency AM signals can be used to adjust these basebandsignals, and reduce the possibility of distortion.

3) Frequency Modulation within a Low-Frequency Channel (FIG. 3c)

In this technique, processor 418 converts each signal derived fromcommunication line 402 to an FM waveform before transmitting the signalonto the selected one of extended pairs 405. It is preferred that thevideo energy be distributed between 3 Mhz and 18 Mhz, as shown in FIG.3c. A 15 Mhz bandwidth is preferred partly because this range issufficiently wide to ensure that the minimum SNR required at thereceiver input is significantly lower SNR than that required by an AMvideo signal. FM transmission also provides extra protection fromcrosstalk interference. These benefits can justify the added expense ofFM modulation in certain situations.

When extended pairs 405 are particularly long, of course, the SNR at thereceiver input will be below that required by 15 Mhz FM signals. In thisevent, bandwidths wider than 15 Mhz can be useful because they willprovide extra sensitivity, i.e., their minimum SNR level will be evenlower. They do, however, suffer greater attenuation because they haveenergy at higher frequencies. If the greater attenuation does not defeatthe extra sensitivity, bandwidths wider than 15 Mhz can extend thetransmission length.

The 3-18 Mhz band is preferred above 15 Mhz bands lower in frequencybecause the advantage of lower bands is small. The attenuationdifference, for example, between 16 and 18 Mhz is approximately 0.5 dBper 100 ft, meaning that only a very small advantage can realized byshifting the low end of the 15 Mhz band from 3 Mhz to 1 Mhz. Theadvantage of the 3-18 Mhz band over a lower band of equal width is areduction in expense of electronics, a reduced likelihood ofinterference from voiceband transients, and less spectral tilt.

As shown in FIG. 3C, the audio is frequency modulated to a frequency of20 Mhz. This frequency was chosen because it is relatively close to thehigh end of the video band, yet not so close to the video that sharpfiltering would be required. Other frequencies, however, can also beused.

Because it requires less SNR at the receiver input, video signalsencoded using FM between 3-18 Mhz (FIG. 3C) can communicate over longerdistances, under some circumstances, than can be achieved using AM witha carrier below 5 Mhz (FIG. 3A). Under other circumstances, the higherfrequencies required by the FM signal will more than cancel thisbenefit.

Following is an illustrative example. At 18 Mhz, telephone wiringattenuates a signal approximately 3.5 dB per 100 feet. That means thatthe energy at the high end of the FM signal will be 10.5 dB lower afterbeing transmitted 300 feet over an extended pair 405. The attenuation ofenergy at 4.5 Mhz, which is near the high end of the AM signal (FIG. 3A)or the unmodulated signal (FIG. 3B) is approximately 3 dB over the samepath (i.e., 1 dB per 100 feet). Thus, after 300 feet, the level of theFM signal of FIG. 3C will be 7.5 dB lower than either of the signals ofFIGS. 3a or 3 b.

Because of its higher sensitivity, however, the level of the FM signalneed only exceed the noise by 30 dB, while AM and unmodulated signalsshould have an SNR of at least 40 dB. Thus, when first fed to thetransmission line, the AM signal will 10 dB closer to its minimumrequired level, which is approximately 0 dB mV for most receivers.Assuming the signals are fed at 30 dB mV, the high end of the FM signalwill be at 19.5 dB mV after 300 feet, while the high end of the AMsignal will be at 27 dB mV. Thus, FM will still have an advantage,meaning it can tolerate, for example, more broadcast interference. Theadvantage, however, has reduced to 2.5 dB, i.e. the advantage of 10 dBhas been eroded by an amount of 7.5 dB. This advantage will disappear ata transmission distance of 400 feet.

Now consider the situation where local network interfaces 404 are notprovided and the transmission path includes 200 feet on extended pairs405 and 100 feet on the part of the local networks 411 that leads tovideo receivers 419. In this situation, the attenuation of transmissionwill be the same but splits may be encountered along the final 100 feet(i.e., the portion of the transmission path that includes a localnetwork 411). Because each split causes 3.5 dB of attenuation, if 8spits are encountered, the FM signal will be at −8.5 dB mV, above itsrequirement of −10 dB mV, while the AM signal will be at −1 dB mV, belowits minimum.

Independent of the transmission path length, the FM signals will be moreresistant to crosstalk interference than AM video signals. At 15 Mhz,for example, the crosstalk loss within a 25-pair bundle of wires variesbetween 25-50 dB, according to measurements made by the inventors. (Asexplained above, crosstalk loss is the energy loss, in dB, suffered by asignal while broadcasting across to neighboring wires.) Thus, if signalstransmit over ten neighboring pairs at similar levels, the interferingenergy contributed by each pair will be 25-50 less than the signal ofinterest, and the total interfering energy will be 10 dB higher, or15-40 dB less than the signal of interest. (This assumes that theinterfering signals are incoherent because they originate from differentsources. The final paragraphs of this section discuss the situationwhere the interfering signals are all the same, i.e., coherent.) FMvideo signals with a 15 Mhz bandwidth, however, can have a capture ratioof approximately 10 dB, eliminating crosstalk as a problem in nearly allcases.

At 5 Mhz, on the other hand, which is the approximate upper frequency ofthe AM signals (FIG. 3A), crosstalk loss varies between 30-60 dB.Because AM signals require at least 40 dB SNR, there is a goodpossibility that this energy will cause interference with the AM signalsat that frequency.

4) Coherent Addition of Crosstalk Energy from Identical SignalsTransmitting over Several Pairs at Once

A particular type of crosstalk interference can occur when transmittingsignals over several twisted pairs in a large bundle of pairs.Specifically, if the signals transmitting over a large group of pairs ina bundle are identical, and one particular pair outside that groupcarries a different signal, then the energy in the multiple pairs may“add coherently” onto the single pair, causing more interference thatwould occur if all pairs carried different signals. Such a situation islikely to occur when a group of signals is made freely available forselection by users at several local networks served by the same bundle.(i.e., when the signals on communication line 402 are not targetedspecifically for one of the units.) In that event, this problem canoccur when the popularity of one signal dominates the others.

An example is where a coaxial cable is brought to the basement of anapartment building, and transceiver/switch 400 derives signals from thatcable, offering any one of 30 video signals to the units therein bytransmission over the telephone wires that lead to the units. Assumethere are 25 units in the building, and 10 of those units select a firstvideo signal. An eleventh unit selects a second video signal. Assumingcrossover loss from any of the ten pairs to the eleventh pair is 30 dB,and the contributions from the ten pairs add coherently, the totalamount of interfering energy on the extended pair carrying the secondsignal will be only 10 db below the level of that second signal, or 20dB higher than the interference from any one of the ten pairs carryingthe first signal. Thus, even if FM is used, there is a high likelihoodof interference with the second signal in this situation. (If thesignals added incoherently, i.e., if all units in the group of tenselected different signals, the total interfering energy would be 20 dBbelow the signal of interest.)

Below we describe a technique which can reduce the increase in crosstalkinterference which occurs in this situation. This technique is embodiedin signal separators 413 and shown in FIGS. 9a and 9 b.

F. Signal Processing, Conversion, and Switching in Transceiver/Switch400 (FIGS. 4-7)

As described above, conversion and switching of signals intransceiver/switch 400 is accomplished by interface processor 418 (FIG.4) and control signal processor 420 (FIG. 7). Processor 418 serves asthe interface between transceiver/switch 400 and communication line 402,and also as the interface between different ones of extended pairs 405.Each of signal separators 413 serves as the interface betweentransceiver/switch 400 and an associated one of extended pairs 405. Assuch, one of the functions of processor 418 is to select and recovervideo and other types of signals from communication line 402, change thecharacteristics of the recovered signals through processing, and applythem to signal separators 413 for transmission to local networks 411 viaextended pairs 405. Another function of processor 418 is to receivevideo and other types of signals from signal separators 413, processthose signals, and transmit them to communication line 402. A thirdfunction of processor 418 is to apply signals received from one ofsignal separators 413 to a different one of signal separators 413.

As emphasized earlier, no processing (such as modulation, demodulation,or frequency shifting) of the signals destined for one of local networks411 takes place after output from processor 418 (along paths 478) andbefore reaching local network interfaces 404. Thus, the signalprocessing performed by processor 418 on the individual signals itselects and recovers from communication line 402 determines thewaveform, frequency, and amplitude at which these individual signalswill be transmitted across extended pairs 405. This processing isdiscussed below.

Control signal processor 420 receives control signals transmitted ontolocal networks 411 (by IR control devices 493) that are targeted formaster controller 415, and it also receives control signals fromcommunication line 402. As described above, processor 420 converts thecontrol signals to a form that can be interpreted by master controller415, and then passes the resulting signals to controller 415. Mastercontroller 415 uses those signals to determine, among other things,which signals shall be selected from communication line 402, and whichof local networks 411 shall be targeted to receive those signals. Thisprocessing is described in detail below.

A detailed description of a preferred embodiment of interface 418 isgiven in the following paragraphs, followed by a description of apreferred embodiment of control signal processor 420. It will beappreciated, however, that processor 418 can take on many differentembodiments, as long as it fulfills the following three functions (whichare also described above):

1) recover video and other signals from communication line 402, andtransmit separate electrical signals, including combinations of therecovered signals, onto each of paths 478 that lead to signal separators413;

2) receive signals transmitted from signal separators 413 along paths479, process these signals, and apply them to communication line 402;

3) receive signals transmitted from signal separators 413 along paths479, process these signals, and apply them to other signal separators413.

There are many ways that processor 418 can be implemented to fulfillthese functions. Indeed, the closed circuit TV industry provides a largevariety of electrical and optical processing devices that couple videosignals, split video signals, modulate and demodulate signals, and shiftsignals in frequency. What is shown herein is a method that is preferredin this application, as well as several alternatives.

1) Processor 418 (FIG. 4)

Referring to FIG. 4, processor 418 includes interface 409, signaldistribution subsystem 403, and signal collection subsystem 407.Interface 409 performs two functions. One is to receive signals fromcommunication line 402 and feed them to subsystem 403 in electricalform, independent of the form at which these signals transmit acrossline 402. (Thus, interface 409 can receive optical signals fromcommunication line 402.) The other function is to receive electricalsignals from signal collection subsystem 407 and to apply them tocommunication line 402, independent of the mode (i.e. electrical,optical, or other) of line 402. (That is, if line 402 is a fiber opticmedium, interface 409 converts electrical signals from sub-system 407 tolight signals.)

There are many examples of devices that perform such a function. Some ofthese are designed to interface between an optical line and anelectrical communication system. One embodiment of interface 409 isshown in FIG. 4a, and is an example of an interface between a coaxialcommunication line 402 and an electrical system. It includes circulator421, block converter 423, and block converter 447.

Circulator 421 receives energy from line 402 and transmits it to blockconverter 423 while isolating the received energy from block converter447. Circulator 421 also receives signals from block converter 447 andapplies them to communication line 402 while isolating block converter423 from these signals.

Block converter 423 selects a particular frequency band from its inputsignal and shifts it in frequency, transmitting the result to signaldistribution subsystem 403. This is done in two steps. First, all inputsignals are heterodyned 423 a, 423 b to shift the selected band to theoutput band. Then, the shifted signal is transmitted through the outputfilter 423 c and passed to subsystem 403. As described later on,subsystem 403 transmits the signals received from interface 409 tosignal separators 413.

Following is an example. Video signals between the frequencies of 54 Mhzand 900 Mhz transmit from line 402 through circulator 421 to blockconverter 423. Converter 423 performs a fixed downshift using a presetheterodyne frequency of local oscillator (L.O.) 423 b of 620 Mhz,shifting the band between 650-700 MHz to the band between 30-80 Mhz. Theresult is passed through a filter 423 c that only passes energy between30-80 Mhz. Thus the frequency band between 650-700 MHz is selected andconverted to the band between 30-80 Mhz. All other frequencies in the 54MHz to 900 MHz band are rejected.

Selection and conversion of a frequency band from communication line 402in the manner described above can be useful when certain frequency bandson a high capacity line are “reserved” for communication with a group ofnetworks. Using the example above, communication line 402 can serve aneighborhood with includes many residences, with the frequencies between650-700 being dedicated to communication with the residencescorresponding to the five local networks 411.

Interface 409 also receives a signal from signal collection subsystem407. This electrical signal, which may include several individualsignals combined together, transmits to block converter 447. Thefrequency shifter 447 a, L.O. 447 b, and band pass filter 447 c in blockconverter 447 combine to shift this signal to the frequency at which itwill transmit across line 402, and amplifier 447 d amplifies the result.Finally, block converter 447 transmits this signal through circulator421 and onto communication line 402.

Following is an example. Video transmitter 417 b receives a signal fromvideo camera 494 b (FIG. 1a ), converts it to a single 20 Mhz FM videosignal between the frequencies of 20-40 Mhz, and transmits it onto localnetwork 411 b. This signal is amplified by local network interface 404 band transmitted across extended pair 405 b. At transceiver/switch 400,the signal transmits to signal separator 413 b (FIG. 2). That componentdirects the signal to signal collection subsystem 407. Video transmitter417 c feeds a second video signal across extended pair 405 c tosubsystem 407 using a similar process. Using techniques described below,subsystem 407 converts these two signals to AM video signals withinadjacent 6 Mhz channels between 120-132 Mhz. These signals aretransmitted over the same conductive path to block converter 447, whichupshifts them to the band between 1000-1012 Mhz, and transmits themthrough circulator 421 to communication line 402.

Signal distribution subsystem 403 receives the electrical signals fromblock converter 423 and, under control of master controller 415 (vialinks 446 a-446 c), selects some of the individual signals containedtherein. Subsystem 403 then creates several different combinations ofthe selected signals. Specifically, a different group of selectedsignals is combined and applied to each of the conductive paths 478.Furthermore, each selected signal is converted to the frequency,waveform, and amplitude at which it will transmit across one of extendedpairs 405. (This conversion also assures that the selected signals ineach group do not overlap in frequency.) These signals transmit to eachof signal separators 413. (As described above, there is a one-to-onecorrespondence between signal separators 413 and paths 478.) Severalembodiments of this selection and combination process are describedbelow. Examples of the signal processing of subsystem 403 will be givenfollowing these descriptions.

Signal separators 413 transmit the signals received from signaldistribution subsystem 403 onto the corresponding one of extended pairs405. Thus, interface 409 and distribution subsystem 403 cooperate todetermine which signals transmit from communication line 402 to localnetworks 411.

In addition to selecting and distributing signals, signal distributionsubsystem 403 also splits the signal received from interface 409,providing that signal to control signal processor 420 over path 420 b.This allows processor 420 to detect signals from communication line 402that are intended to communicate with master controller 415. As will bedescribed below, processor 420 selects specific signals from path 420 bby demodulating the energy within a specific frequency band. It thenprocesses the resulting signal, and feeds it to master controller 415.

Except for control signals that provide communication with mastercontroller 415, subsystem 407 receives all non-telephone signals thatsignal separators 413 receive from extended pairs 405. (Non-telephonesignals are those not intended to communicate with local exchange 475.)These signals transmit from signal separators 413 to subsystem 407 alongpaths 479. Subsystem 407 selects particular signals from among thosearriving on paths 479 and combines them onto a single conductive path.(Before combination, signals may be shifted in frequency to prevent themfrom overlapping in frequency and to arrange them within adjacentchannels for application to communication line 402.) This combinedsignal is transmitted to interface 409, as described above.

A detailed description of several embodiments of signal distributionsubsystem 403 and signal collection subsystem 407 is presented next.

2) Signal Distribution Subsystem 403 a (FIG. 5a)

Signal distribution subsystem 403 a, one preferred embodiment of signaldistribution subsystem 403, is shown in FIG. 5a. As described above,interface 409 transmits signals along a single conductive path leadingto signal distribution subsystem 403 a. Internal to subsystem 403 a,these signals transmit to splitter 426′, which splits the signal energyalong several conductive paths. Four paths are contemplated in FIG. 5a.Three paths lead to demodulators 426 a-426 c, (collectively,demodulators 426). The fourth path, labelled path 420 b, leads to signalprocessor 420.

Processing of the output of splitter 426′ by demodulators 426 isdescribed in the following paragraphs. Processing of this output bycontrol signal processor 420 is described further on in this disclosure.

Each demodulator 426 (details are shown for demodulator 426 c only)selects one signal from among those applied by block converter 423, andconverts that signal to baseband. The selection and conversion processconducted by demodulators 426 is similar to that performed by ordinarycable converters that have baseband outputs. As shown in FIG. 5a, theinput signal is frequency shifted by multiplication with the outputfrequency of a local oscillator. (A local oscillator is denoted by“l.o.” in the figures of this disclosure.) The local oscillatorfrequency is tuned to bring the selected signal to an intermediatechannel. The shifted signal is then filtered, isolating the intermediatechannel. Finally, this signal is demodulated, generating the selectedsignal at baseband.

The identity of the signal selected by demodulators 426 is determined bymaster controller 415. That component implements its control by sendingsignals along link 446 a to each of demodulators 426. These signalsdetermine the frequency of the local oscillators of those components,thus determining which signals are brought to the intermediate channelby each demodulator 426. Ordinary techniques that achieve digitalcommunication between two components on an electronic circuit board cansuffice for link 446 a.

Under an alternative embodiment, the selection of an individual signalfrom communication line 402 is predetermined by the hardware instead offalling under the control of master controller 415. This can be donesimply by designing or manually adjusting demodulators 426 to demodulateonly signals within a specific channel. Selection is then determined atthe “headend” by feeding the desired signal onto line 402 at thechannels to which demodulators 426 are tuned. For example, assume thatcommunication line 402 is a cable TV feed and that 100 NTSC videosignals pass through circulator 421 to block converter 423 in interface409 a. Assume further that block converter 423 selects the 10 adjacentsignals beginning at 300 Mhz and converts them to the 10 adjacent 6 Mhzbands between 108 Mhz and 168 Mhz. Now let demodulator 426 a be designedto always select the video signal expressed between 108 and 114 Mhz,whatever that signal may be. In this situation, the identity of thesignal selected by demodulator 426 a is determined at the “headend,” orroot of the cable TV feed. Specifically, whatever signal is fed between300-306 Mhz at the root will be selected and provided as output bydemodulator 426 a.

The basebanded signals output by demodulators 426 constitute the signals“selected” for distribution to local networks 411. (They are labelledthe “selected” signals in FIG. 5a.) They will pass through separators413 to extended pairs 405. First, however, they are converted to thewaveform, frequency, and energy level at which they will be transmittedacross extended pairs 405. This is accomplished by modulators 410 a-410d (collectively, 410).

Each modulator 410 (the details of modulator 410 d are shown) isdesigned or manually adjusted so that it always modulates its input inthe same manner, outputting it within the same frequency band and at thesame energy level. Thus, each of modulators 410 corresponds to adifferent “channel” used by signals that transmit across extended pairs405. To provide flexibility in assigning any one of the signals selectedby demodulators 426 to any of the channels created by modulators 410,signals from demodulators 426 transmit to modulators 410 through switch462 a. Thus, switch 462 a assigns the selected signals to differentchannels.

Switch 462 a works as follows. Internal to switch 462 a are splitters435 a-435 c (collectively, splitters 435), which have a one-to-onecorrespondence with demodulators 426. As shown in FIG. 5a, each of thesignals from demodulators 426 transmits to splitters 435 which splitsthe energy of the signals onto four paths, each one leading to adifferent one of switching banks 448 a-448 d (collectively, banks 448).Each bank 448 responds to signals sent from master controller 415 alonglink 446 b. In response to these signals any one of banks 448 can switchany one of its inputs to any or all of modulators 410 a-410 d. Thus,switch 462 a can provide each of modulators 410 with the outputs of anydemodulator 426. Because the outputs of demodulators 426 are all atbaseband, however, master controller 415 ensures that at most one signal(i.e., the output of only one demodulator 426) is provided to any one ofmodulators 410 at one time. Some of modulators 410, however, may notreceive signals.

As described above, each modulator 410 converts the baseband signal itreceives to a particular waveform, frequency, and energy level. Thesignals output by modulators 410 do not undergo further processing(modulation or frequency shifting) before exiting subsystem 403. Asdescribed earlier, the waveform, frequency, and energy level of signalsoutput by subsystem 403 a is very important because these signalsultimately transmit to extended pairs 405 without any further processingexcept for filtering and switching. Thus, the processing applied bymodulators 410 determine, to a large extent, the reliability oftransmission to local networks 411.

As described in the first CIP application, when AM signals aretransmitted with a picture carrier below 5 Mhz, spectral tilt is likelyto cause distortion. One of the proposed solutions is to “pre-emphasize”the high frequencies of the signal so that the attenuation related totransmission will result in reception of a signal with a flat spectrum.It is preferred that this pre-emphasis be performed within modulators410. Following is an example of how pre-emphasis can be implementedwithin modulator 410 a.

Assume that modulator 410 a outputs an AM NTSC video signal with apicture carrier at 1.25 Mhz (FIG. 3a). The upper sideband of such asignal will extend approximately between 1.25 Mhz and 5.25 Mhz. Assumethat attenuation of extended pair 405 b at 1.25 Mhz is 1 dB per 100feet, and at 5.25 Mhz it is 3 dB per 100 feet. (Assume further that theaffect of attenuation follows, to a good approximation, a linearvariation between those endpoints.) If extended pair 405 b is 1000 feetlong, and the signal from modulator 410 a is to be applied to pair 405b, the energy at 5.25 Mhz would ordinarily be received at a level 20 dBlower than that at 1.25 Mhz. To compensate for this, processor 410 a caninclude circuitry to “pre-emphasize” the signal such that energy at 5.25Mhz is transmitted 20 dB higher than that at 1.25 Mhz, and such that thepre-emphasis varies approximately linearly between those frequencies.Such pre-emphasis circuitry is known.

It is preferred that the modulation process follow any pre-emphasisprocess. This sequence is shown in the block diagram of modulator 410 d(FIG. 5a). If AM waveforms are used, the modulation process involvesmixing or multiplying the frequency of the signal by a local oscillator.If FM waveforms are used, the modulation process involves “encoding”voltage variations of the signal as frequency deviations of the carrier.After modulation, the signal is filtered and amplified to the level atwhich it will transmit across the wiring.

Each signal produced by modulators 410 transmits through switch 401 overone or more of paths 478 to signal separators 413. (Paths 478 have aone-to-one correspondence with signal separators 413, and thus withextended pairs 405 and local networks 411.) Switch 401, which respondsto commands from master controller 415 sent over link 446 c, isimplemented in the same manner as switch 462 a. Master controller 415,however, allows switch 401 to apply the output of more than onemodulator 410 onto any one of paths 478 a-478 c. Thus, switch 410“composes” the signal sent to each of signal separators 413 by combiningthe outputs of modulators 410. The only restriction is that the signalsfrom two of modulators 410 that overlap in frequency cannot be switchedonto the same one of paths 478. The signals output by switch 401 arelabelled “distributed signals” in FIG. 5a.

3) Signal Collection Subsystem 407 a (FIG. 6a)

Signal collection subsystem 407 a, one preferred embodiment of signalcollection subsystem 407, is shown in FIG. 6a. Signals received bysubsystem 407 a arrive along paths 479 and transmit to amplifiers 408a-408 c (collectively, amplifiers 408). These signals originate on localnetworks 411.

Following is an example of the transmission path followed by a signalreceived by subsystem 407 a. Signals fed by video transmitter 417 b tolocal network 411 b are received by local network interface 404 b andretransmitted onto extended pair 405 b. These signals transmit acrosspair 405 b to signal separator 413 b. As is described later on, signalseparator 413 b separates out the telephone signals and passes theremaining signals to amplifier 408 b. Equivalent paths are used by otherRF transmission devices to send signals to amplifiers 408 a and 408 c.

The output of each amplifier 408 passes through switch 429 todemodulators 416 a-416 d (collectively, demodulators 416). Amplifiers408 are provided to compensate for the energy loss caused by signalsplitting internal to switch 429.

The design of switch 429 follows that of switch 462 a in FIG. 5a. Assuch, switch 429 responds to commands from master controller 415. Thesesignals are sent over link 446 d.

Each demodulator 416 selects a channel (i.e. a frequency band) from itsinput signal and converts the energy in that band to basebandfrequencies. As shown for demodulator 416 a, the demodulation procedureinvolves frequency shifting a selected frequency band to an intermediateband, filtering that band, and demodulating the result. Equalization ofthe signal to compensate for spectral tilt is also performed, ifnecessary. In the case of AM signals, it is preferred that theequalization be done after demodulation. In the case of FM signals,equalization should be done before demodulation but after filtering. Thepurpose of equalizing FM signals before demodulation is described in thefirst CIP application. (This equalization process is not to be confusedwith the process called “emphasis” which is part of standard FMcommunication. In this process, the level of the higher frequencies ofthe information signal are amplified before modulation, and thenattenuated after demodulation. This compensates for the tendency,inherently part of FM communication, whereby noise affects the higherfrequencies of a signal more than the lower frequencies.)

The demodulation process creates a basebanded version of the signal inthe selected band. Selection of channels by demodulators 416 is done byaltering the frequency of the local oscillator (l.o.) used to implementfrequency shifting. This frequency is set in response to control signalsfrom master controller 415 transmitted over link 446 e.

The output of each demodulator 416 constitutes the signals “collected”from local networks 411. These signals are passed to modulators 428a-428 d (collectively, modulators 428), which have a one-to-onecorrespondence with demodulators 416. As is described below, modulators428 perform the first step in “exporting” signals by applying them tocommunication line 402.

As is also described below, in embodiments in which local networks 411transmit video signals to each other, signal distribution subsystem 403b (FIG. 5b) is used in place of subsystem 403 a, and the “collected”signals are passed along paths 488 a-488 d (collectively, paths 488) tosignal distribution subsystem 403 b. Subsystem 403 b can transmit eachsignal received from paths 488 to a local network 411 that is differentfrom the local network that originated the signal.

By controlling switch 429 and demodulators 416, master controller 415determines which of the signals input to amplifiers 408 are “collected,”i.e. output from one of demodulators 416. Note that switch 429, becauseit follows the design of switch 462 a, can simultaneously connect theoutput of every amplifier 408 to any number of demodulators 416. This isimportant if the signal provided by one of amplifiers 408 includes morethan one independent signal. For example, if the energy output byamplifier 408 b includes two adjacent 6 Mhz NTSC video signals between6-18 Mhz, and the output of amplifier 408 b can be switched to bothdemodulators 416 b and 416 c, both video signals can be “collected.”Note that none of demodulators 416 can receive the output of more thanone of amplifiers 408, even if the two output signals do not overlap infrequency. Such switching would not make sense because demodulators 416select only one signal at a time.

As described earlier, modulators 428 implement the first step inapplying the outputs of demodulators 416 to communication line 402.Specifically, each of modulators 428 receives the single basebandedsignal output by the corresponding one of demodulators 416. As shown inFIG. 6a, the process includes mixing the frequency of a local oscillator(l.o.) with that of the input signal, and filtering the output. Thisprocess creates a new signal, with identical information content, withinan RF frequency band.

The local oscillators used by each of the modulators 428 are such thatthe resulting output frequency bands do not overlap. This allows theoutputs to be combined onto a single conductive path. In a preferredembodiment, the frequency bands confining the outputs of modulators 428are adjacent in addition to being non-overlapping. This minimizes thewidth of the band occupied by the combined signal.

The signals output by modulators 428 are all transmitted to coupler428′. That component combines the individual signals onto a singleconductive path, and passes it to interface 409. That component appliesthe combined signal onto communication line 402, as described above.

4) Control Signal Processing (FIG. 7)

Referring to FIG. 7, processor 420 includes filters 427 a-427 c and 427z (collectively, filters 427), demodulators 443 a-443 c and 443 z(collectively, demodulators 443), and digitizer 436.

As described above, control signals generated by individual controldevices 493 and targeted for master controller 415 are transmitted ontolocal networks 411 by video receivers 419, received by interfaces 404,and fed to extended pairs 405. The control signals are recovered fromextended pairs 405 by signal separators 413 and routed to control signalprocessor 420 along paths 477, which have a one-to-one correspondencewith signal separators 413. The control signals arrive at processor 420at the frequency and waveform at which they were fed to extended pairs405.

Control signals from communication line 402 also transmit to processor420. These signals are transmitted from signal distribution system 403along path 420 b (FIG. 4).

As seen in FIG. 6, path 420 b connects to filter 427 z, while signalstransmitting over paths 477 present at corresponding filters 427 a-427c. Filters 427 restrict the frequency of the signals passing to thecorresponding demodulators 443 to the bands used by the control signalstargeted for master controller 415. Signals passing through filter 427 zare received by demodulator 443 z, while signals passing through filters427 a-427 c are received by demodulators 443 a-443 c.

Demodulators 443 a-443 c and 443 z convert such received signals tobaseband frequencies, and pass the results to digitizer 436. That deviceconverts the basebanded signals to digital signals, and passes them tomaster controller 415 over path 420 a. Common methods for communicatingdigital information between two components on a circuit board cansuffice for this link. Methods of digitizing and communicating controlsignals originating from infrared transmitters are described in detailin the second CIP application.

5) Example #1

Referring to FIGS. 1a, 2, 4, 4 a, 5 a, 6 a, and 7, the following is anexample of the processing of non-telephone signals in transceiver/switch400. Assume that line 402 is a fiber optic cable transmitting highfrequency optical impulses that represent frequency modulated encodingof a group of signals with a bandwidth of 5,000 Mhz. Among theindividual signals expressed in the 5,000 Mhz band are 50 standardamplitude modulated NTSC signals confined within adjacent 6 Mhzchannels. These are expressed between the frequencies of 2000 Mhz and2300 Mhz.

One of the functions of the communication system of this invention is totransmit any of the individual signals expressed between 2000-2500 Mhzon demand to video receivers 419 and transceiver 491 c connected tolocal networks 411 a-411 c. Furthermore, the system must allow the usersto indicate their video selections by using infrared remote controltransmitters 493 a, 493 b, and 493 c shown in FIG. 1a.

Communication line 402 also accommodates communication of signals in theopposite direction, away from transceiver/switch 400. A second task ofthe communication system is to allow video transmitters 417 andtransceiver 491 c to transmit signals onto line 402.

The light impulses from communication line 402 are received by interface409. That component responds to these impulses by producing a frequencydemodulated electrical version of the 5000 Mhz signal encoded therein.Block converter 423 in interface 409 a selects the frequencies between2000 Mhz and 2500 Mhz, and converts them to voltage variations between100 Mhz and 600 Mhz.

The 500 Mhz wide, composite electrical signal provided by interface 409is transmitted to splitter 426′ in signal distribution subsystem 403 a.Splitter 426′ splits the input energy four ways, transmitting the signalto demodulators 426 and also along path 420 b to control signalprocessor 420.

Referring also to FIG. 8, demodulators 426 react in the followingmanner. In response to signals fed from master controller 415 over link446 a, demodulator 426 a selects and basebands the signal between 176Mhz and 182 Mhz (video signal U). Similarly, demodulator 426 b selectsand basebands the 6 Mhz AM signal between 188-194 Mhz (video signal V),and demodulator 426 c selects the signal between 200-212 Mhz, which is adigital signal conforming to the “10BaseT Ethernet” standard (digitalsignal Y), and converts it to a demodulated signal at baseband. Thus,two ordinary NTSC video signals are selected from line 402, basebanded,and provided to switch 462 a along two separate conductive paths. Athird conductive path provides a 12 Mhz wide computer signal.

Switch 462 a applies the output of demodulator 426 a (video signal U)onto the path leading to modulator 410 a, the output of demodulator 426b (video signal V) onto the paths leading to modulators 410 b and 410 d,and the output of demodulator 426 c (digital signal Y) onto the pathleading to modulator 410 c.

Modulators 410 modulate their input signals, converting them tofrequency bands between 1 Mhz and 22 Mhz. These are the frequencies usedto transmit signals from transceiver/switch 400 to local networks 411.Specifically, modulators 410 a and 410 b amplitude modulate videosignals U and V, respectively, to produce RF signals at 40 dB mV between1-6 Mhz in each case. (The frequency band between 1 and 6 Mhz can beused to provide a standard 6 Mhz NTSC channel if the part of the lowervestigial sideband between 0-1 Mhz is filtered out. This technique isdescribed in the second CIP application.) Modulator 410 d, on the otherhand, converts video signal V to an FM signal at 40 dB mV between 7 and22 Mhz, and modulator 410 c converts digital signal Y to a signalconfined between 6 and 18 Mhz. Switch 401 receives the outputs ofmodulators 410 a-410 c and applies them to paths 478 a-478 c,respectively. Switch 401 also applies the output of modulator 410 d topath 478 a and couples the output of modulator 410 b onto path 478 c.Thus, path 478 a conducts both video signal U and video signal V (indifferent frequency bands), path 478 b conducts video signal V, and path478 c conducts both video signal V and digital signal Y (in differentfrequency bands).

The signals applied to paths 478 a-478 c transmit to signal separators413 a-413 c, respectively. Those components feed the signals ontoextended pairs 405 a-405 c, respectively, using techniques describedbelow.

The signals transmit across pairs 405 a-405 c to local networkinterfaces 404 a-404 c, respectively, each of which converts the signalsas necessary to enable them to be transmitted over respective localnetworks 411 a-411 c. Specifically, local network interface 404 aconverts video signal V to an AM signal in the frequency band between24-30 Mhz and video signal U to an AM signal in the frequency bandbetween 12-18 Mhz. Meanwhile, local network interface 404 b convertsvideo signal V to an AM signal in the frequency band between 54-60 Mhz(corresponding to VHF channel 2). Finally, local network interface 404 cconverts video signal V to the AM signal between 12-18 Mhz, andexpresses digital signal Y between the frequencies of 18-40 Mhz.Techniques to perform these conversions are described below.

After this conversion, local network interfaces 404 amplify the signalsand retransmit them onto the respective local networks 411. Once appliedto local networks 411, signals U, V, and Y are received by videoreceivers 419 and transceiver 491 c. Video receivers 419 convert signalsV and U to tunable frequencies before transmitting them to connectedtelevisions 492, and transceiver 491 c converts its signal to a formappropriate for computer 495 c. Video receivers 419 a and 419 a′, inparticular, apply a single upshift of 186 Mhz to energy between thefrequencies of 12 Mhz and 30 Mhz, converting signals U and V to videosignals with picture carriers at 199.25 and 211.25 Mhz, (i.e. VHFchannels 11 and 13), respectively. A design for a video receiver thatperforms such a block conversion is given in the second CIP application,and a design for transceiver 491 c is given in the first CIPapplication. These conversions allow users at local networks 411 a and411 b to watch video signal V, those at local network 411 a can alsowatch video signal U, and computer 495 c at local network 411 c canreceive digital signal Y, which is an “EtherNet” signal fromcommunication line 402.

Meanwhile, RF transmitters 417 connected to local networks 411 applysignals to those networks that transmit in the opposite direction. Theseare received by interfaces 404, which in turn apply them to pairs 405.The signals then transmit to signal separators 413 in transceiver/switch400. Those components direct the signals along paths 479 to amplifiers408 in collection subsystem 407 a of processor 418. All of these signalstransmit across extended pairs 405 at frequencies between 24 and 100Mhz, a band that does not overlap with the band in which signalstransmit in the opposite direction (i.e., 1 Mhz-22 Mhz).

(Techniques embodied in local networks interfaces 404 that receivesignals from local networks 411, convert them, and transmit them acrossextended pairs 405 are described below. The routing of these signals bysignal separators 413 is also described below.)

An example of the signals transmitted by the RF transmitters 417connected to local networks 411 and the conversions performed by localnetwork interfaces 404 follows. Assume that video transmitter 417 binputs an NTSC video signal (video signal W) from camera 494 b and feedsit onto local network 411 b amplitude modulated between 6-12 Mhz. Thissignal is received by local network interface 404 b, converted to an FMsignal between 24-54 Mhz, amplified, and applied to extended pair 405 b.At transceiver/switch 400, video signal W transmits to signal separator413 b, which applies it to amplifier 408 b. Meanwhile, video signal X isgenerated by camera 494 c and transmits from video transmitter 417 c toamplifier 408 c in an identical manner (via interface 404 c, extendedpair 405 c, and signal separator 413 c).

Transceiver 491 c, meanwhile, receives a digital signal from computer495 c. That signal carries 1 Mbits/sec of information, (less thandigital signal Y) and is called digital signal Z. Transceiver 491 cexpresses this signal between 1-6 Mhz, and applies it to local network411 c where it is intercepted by local network interface 404 c.Interface 404 c encodes this signal using frequencies between 54-100 Mhzand transmits it onto extended pair 405 c. The signal transmits acrossto transceiver/switch 400. Because it is expressed at relatively highfrequencies, signal Z is received with a lower SNR, but its widerbandwidth allows reception with a low error rate. At transceiver/switch400, digital signal Z transmits through signal separator 413 c toamplifier 408 c.

The signal reaching amplifier 408 c covers the frequencies between 24Mhz to 100 Mhz and includes both video signal X and digital signal Zfrom local network 411 c. Under instructions from master controller 415,switch 429 directs the output of amplifier 408 c to both of demodulators416 b and 416 c. Meanwhile, video signal W reaches amplifier 408 b. Uponoutput from amplifier 408 b, switch 429 directs that signal todemodulator 416 a.

Under the control of controller 415, each demodulator 416 b, 416 cprocesses only one of the two individual signals that constitute theirinputs. Specifically, demodulator 416 b demodulates video signal X,providing it at baseband frequencies to modulator 428 b, while processor416 c demodulates digital signal Z, providing it at baseband frequenciesto modulator 428 c. Processor 416 a, meanwhile, demodulates video signalW, providing it at baseband frequencies to modulator 428 a.

(These signals also transmit along paths 488. Because signaldistribution subsystem 403 a is not equipped to input signals from thesepaths, however, signals transmitting along paths 488 are not received.)

Modulators 428 convert their inputs to RF frequencies. Specifically,modulator 428 a converts video signal W to a modulated form between400-406 Mhz. Similarly, modulator 428 b converts video signal X to amodulated form between the frequencies of 406-412 Mhz, and modulator 428c converts digital signal Z to a modulated form between the frequenciesof 412-424 Mhz.

These three signals are fed to coupler 428′. That component combines thethree signals and transmits them to interface 409. Interface 409 thenencodes the energy between 400-424 Mhz in this input signal into lightimpulses which it applies to communication line 402.

Control signals are also transmitted from local networks 411 totransceiver/switch 400. At local networks 411 a, control signal A isintroduced by IR remote control transmitter 493 a in the form of lightpatterns. These are detected by video receiver 419 a, converted to anelectrical signal with a 0.5 Mhz bandwidth centered at 23 Mhz, and fedonto local network 411 a. Control signal A is then intercepted by localnetwork interface 404 a and fed onto extended pair 405 a between thefrequencies of 22.75-23.25 Mhz. It transmits to transceiver switch 400,passing through signal separator 413 a to paths 479 a and 477 a. Path479 a leads to amplifier 408 a. Although this path may connect to one ofdemodulators 416, control signal A will transmit no further becausedemodulators 416 do not demodulate signals in the band between22.75-23.25 Mhz.

Control signal A transmits across path 477 a through filter 427 a todemodulator 443 a in control signal processor 420 (FIG. 7). Thatcomponent basebands the signal, passing it to digitizer 436 whichconverts the signal to digital form. Finally, this digitalrepresentation of control signal A is transmitted to master controller415. Control signals B and C are created by IR remote controltransmitters 493 b and 493 c and transmit to master controller 415 in asimilar manner using the same frequencies.

Following is an example of a change in channel selection. As explainedabove, video signal U is part of the 5000 Mhz signal transmitting online 402. Specifically, assume that video signal U spans the frequenciesbetween 2076 Mhz and 2082 Mhz, which are translated by interface 409 tothe band between 176-182 Mhz. This band is selected when demodulator 426a converts it to the “intermediate” frequency. In response to a controlsignal from local network 411 a, however, master controller 415 caninstruct demodulator 426 a to demodulate a different channel, such asthe one between 182 Mhz and 188 Mhz, thereby “assigning” a new channelto video signal U.

FIG. 8 shows a table which summarizes the signals, transmissiondirection, and channels used for the communication described in thisexample.

G. Transmitting Signals from one Local Network to a Second Local Network(FIGS. 1 b, 5 b)

Signal distribution subsystem 403 b, an alternative embodiment of signaldistribution subsystem 403, is shown in FIG. 5b. There are only twodifferences between this embodiment and that of subsystem 403 a. One isthat switch 462 b replaces switch 462 a. The second difference is thatsignals from signal collection subsystem 407 a (FIG. 6a) transmit atbaseband along paths 488 to switch 462 b, providing four extra inputs tothat switch. Thus, switch 462 b can (under the direction of mastercontroller 415 via link 446 b) provide signals recovered from localnetworks 411, in addition to signals provided from communication line402, to modulators 410. This allows communication between the localnetworks 411.

Following is an example of communication conducted by a system thatincludes signal distribution subsystem 403 b. Referring to FIG. 1b, aprivate telephone network connecting offices 512 a-512 e (collectively,offices 512) is established by PBX (“private branch exchange”) 500 andextended pairs 405 a-405 e that connect between each office and PBX 500.PBX 500, which is located in wiring closet 501, also connects to localexchange 475 (i.e. the public telephone network) through cable 475′,which provides two lines of service. Such a configuration represents atypical office telephone system.

Transceiver/switch 400 (FIG. 2) is also located inside wiring closet501, interposing along the portions of extended pairs 405 that is withina few (e.g., 20) feet of PBX 500. The relatively short portions ofextended pairs 405 connecting between transceiver/switch 400 and PBX 500are called twisted pairs 476 a-476 c (collectively, 476). High capacitycommunication line 402 also connects to transceiver/switch 400.

Internal to each of offices 512 are several types of communicationdevices. (The communication devices connected to offices 512 d and 512 eare not shown because the system shown in FIG. 1b provides onlytelephone communication with those offices.) Two of these, telephonedevices 514 a-514 c (collectively, telephone devices 514) and videotransceivers 509 a-509 c (collectively, video transceivers 509), connectdirectly to the corresponding one of extended pairs 405. The wiring thatconnects these devices to the extended pairs 405 a-405 c is shown aslocal networks 511 a-511 c, respectively. Thus, in FIG. 1b, thetelephone wiring that comprises each local network 511 is simply twoshort telephone cables connecting to the associated extended pair.

Each telephone device 514 connects to the associated local network 511via a low-pass filter (LPF). As described in the first CIP application,these filters prevent telephone devices 514 from affecting RF energy onthe local networks 511. (These filters may be provided as part ofsplitter 161, which is described in the first CIP application.)

Each video transceiver 509 connects to the corresponding one of extendedpairs 405 to transmit and receive video signals. Video transceivers 509also detect infrared signals, convert them to electrical signals, andfeed them onto the extended pairs 405. Individually, each of theseprocesses is described in the parent and first CIP applications. Thefirst CIP application also describes how to combine RF transmitters andreceivers into a single device that communicates through a singleconnection to active telephone wiring.

Video signals received by transceivers 509 are passed to video displays508 a-508 c (collectively, video displays 508). Video sources 507 a-507c (collectively, video sources 507) also connect to video transceivers509. Video sources 507 are devices such as video cameras, VCRs, ordigital devices, that create electronic signals containing theinformation necessary to display the type of video pictures addressed inthis disclosure. These signals are passed to the connected one of videotransceivers 509. The components in offices 512 d and 512 e are notshown.

Video sources 507 a, 507 b, and 507 c each create a single video signal,called video signals Va, Vb, and Vc, respectively. These signals are fedto video transceivers 509 a, 509 b, and 509 c. Using amplitudemodulation, video transceivers 509 convert their input signals,expressing them between the frequencies of 1 Mhz and 6 Mhz, according tothe spectral distribution shown in FIG. 3a. (As noted earlier, AM videosignals may suffer from crosstalk interference, even at very lowfrequencies. Thus, the use of AM in this example is arbitrary, and theuse of FM may be indicated if the crosstalk loss is small.) Thesesignals are then transmitted onto the network 511 of twisted pair wiringinternal to offices 512 a, 512 b, 512 c, respectively.

Because local network interfaces 404 are not provided, the signalsapplied by video transceivers 509 to local networks 511 transmitdirectly onto extended pairs 405 a-405 c. If the wiring internal to theoffice is a single wire, this wiring can be simply be considered anextension of extended pairs 405 a-405 c.

The signals applied to extended pairs 405 transmit to signal separators413 in transceiver/switch 400 (FIG. 2). Signal Va is routed by signalseparator 413 a to both filter 427 a in control signal processor 420(FIG. 7), and amplifier 408 a in subsystem 407 a of processor 418 (FIG.6a). Signal Va is blocked by filter 427 a, but is transmitted byamplifier 408 a through switch 429 to demodulator 416 a. That componentdemodulates signal Va, passing it along path 488 a to signaldistribution subsystem 403 b. In a similar manner, signals Vb and Vc areapplied at baseband to paths 488 b and 488 c.

Control signals are also transmitted from offices 512. These controlsignals are infrared (IR) signals issued by infrared transmitters notshown in the figures. Using techniques described in the parent and firstCIP application, the IR signals are detected by video transceivers 509,converted to electrical signals, and transmitted onto local networks511. These signals are applied to extended pairs 405 and transmit tosignal separators 413 following the same routes, described above,followed by the video signals. Control signals from video transceiver509 c, for example, are routed by signal separator 413 c to both filter427 c in control signal processor 420, and amplifier 408 c in subsystem403 b. These signals are demodulated by demodulator 443 c, digitized bydigitizer 436, and transmitted to master controller 415.

As described above, video signals Va, Vb, and Vc, transmit along paths488 to switch 462 b in subsystem 403 b. That component switches thesesignals, connecting Va to modulator 410 a, Vb to modulator 410 b, and Vcto modulator 410 c. Using frequency modulation, modulators 410 a-410 cexpress their inputs signals between the frequencies of 7-22 Mhz. Thesesignals are all applied to switch 401.

Switch 401 switches signal Vb (output by modulator 410 b) onto paths 478a and 478 c, and signal Vc onto path 478 b. Thus, these signals transmitthrough signal separators 413 and across extended pairs 405 arriving atoffices 512. Because of the connections made by switch 401, signal Vb(originating in office 511 b) transmits to offices 512 a and 512 c, andsignal Vc (which was sent from office 511 c) transmits to office 512 b.Internal to offices 512, video transceivers 509 receive these signalsand provide them to video displays 508.

It is thus apparent that the system just described allows workers inoffices 512 a and 512 c to hold a video conference with a worker inoffice 512 b. Initially, the workers in office 512 a and 512 c watch theworker in 512 b, while the worker in office 512 b watches the worker inoffice 512 c. By sending a control signal to master controller 415, asdescribed above, the worker in office 512 b can switch to display thesignal from office 512 a. This is done as follows. In response to asignal from office 512 b, master controller 415 sends a signal to switch401, instructing it to connect the output of modulator 410 a to path 478b instead of connecting the output of modulator 410 c to path 478 b.Because modulator 410 a provides signal Va on output, this effects thedesired switching.

Now assume communication line 402 is a coaxial cable that carries three6 Mhz video signals between the frequencies of 200-218 Mhz. A worker inoffice 512 b can also select a video signal from communication line 402from transmission to his or her office. This is done in the followingmanner.

Signals between 200-218 Mhz on communication line 402 transmit tointerface 409 a where they pass through circulator 421 to blockconverter 423. That component downshifts these signals to thefrequencies between 54 and 72 Mhz, and passes them through splitter 426′in subsystem 403 b to demodulators 426. Next, a control signal is sentfrom video transceiver 509 b to master controller 415, as describedabove. In response to this signal, master controller 415 directsdemodulator 426 a to demodulate the signal between 60 Mhz and 66 Mhz,providing it at baseband to switch 462 b. In response to another signalfrom master controller 415, switch 462 b connects this signal tomodulator 410 d. Finally, master controller 415 commands switch 401 toconnect the output of modulator 410 d (rather than the output ofmodulator 410 a) to path 478 b. Because signals passed to path 478 btransmit, as described above, to office 512 b, the desired signalswitching is achieved.

H. A Third Embodiment of Signal Distribution Subsystem 403 (FIG. 5 c)

Signal distribution subsystem 403 c, which represents a third embodimentof signal distribution subsystem 403, is shown in FIG. 5c. In thisembodiment, the demodulation and modulation processes are combined, andonly one switch is provided. This has several advantages, which aredescribed below.

Signals transmitted from interface 409 are divided by splitter 426′along five paths. Four paths lead respectively to RF processors 485a-485 d (collectively, RF processors 485). The fifth path, labelled path420 b, leads to signal processor 420. The processing of these signals byRF processors 485 is described in the following paragraphs. Theprocessing by control signal processor 420 is described in an earliersection of this disclosure.

Each RF processor 485 selects a channel from among the multiple channelsthat comprise its input signal and converts the selected channel to thewaveform, frequency, and amplitude at which it will transmit through asignal separator 413 and across an extended pair 405. As shown in FIG.5c, in the first part of this process a selected frequency band isshifted to an intermediate band (using a frequency shifter and localoscillator) and the result is filtered and then demodulated. Thiscreates a basebanded version of the selected signal. (Demodulation of anAM signal involved a process called “detection,” while demodulation ofan FM signal requires a process called “decoding.”)

Selection of channels in RF processors 485 is achieved by tuning thefrequency of the local oscillator (l.o.) This is done in response tosignals from master controller 415, which are sent over link 446 a.

After demodulation, a pre-emphasis process is optionally performed onthe basebanded signal to compensate for spectral tilt. As describedabove and in the first CIP application, this process amplifies thehigher frequencies to compensate for the greater attenuation of thosefrequencies during transmission. After pre-emphasis, the signal ismodulated to its final waveform and frequency. (If AM waveforms areused, the modulation process involves mixing the signal with thefrequency of a local oscillator. If FM waveforms are used, themodulation process involves “encoding” voltage variations of the signalas frequency deviations of a carrier provided by the local oscillator.)After modulation, the signal is amplified and applied to switch 487.

As described above, each RF processor 485 selects one signal from itsinput channels and provides that signal at an RF channel. Thus, RFprocessors 485 are similar to ordinary “cable converters” that receive aband of multiple video signals, select one channel, and output thesignal within an different RF channel.

The signals exiting RF processors 485 are labelled “selected signals” inFIG. 5c. Each one will be transmitted to a single signal separator 413,and thus will be transmitted over exactly one extended pair 405. Theassignment of the outputs of RF processors 485 to signal separators 413is accomplished by switch 487 under the control (via link 446 c) ofmaster controller 415.

Switch 487 receives the selected signals from RF processors 485, andswitches them over paths 478 a-478 c to signal separators 413 a-413 c.The design and operation of switch 487 is similar to that of switch 462a. As such, switch 487 responds to control signals sent from mastercontroller 415. These signals are transmitted over link 446 c. Mastercontroller 415 may connect the output of several of RF processors 485 tothe same one of paths 478. Master controller 415 must ensure, in thatcase, that these outputs do not overlap in frequency.

Subsystem 403 c is efficient for systems in which it is unusual to haveduplication within the group of signals selected to be sent to localnetworks 411. Provision of cable TV signals to a small apartment unit isa good example of such a situation. Assume, for example, thatcommunication line 402 carries 60 cable TV signals to a 20 unitapartment house, and that an embodiment of the communication systemdisclosed herein was installed to provide a single signal to each ofthose units. This requirement could be satisfied if the embodimentincluded subsystem 403 c and 20 RF processors 485. It should be clear,furthermore, that any embodiment with fewer than 20 demodulators (whichare used for channel selection) and 20 modulators would not suffice.(Specifically, they would fail whenever the 20 units each requested adifferent one of the 60 signals.)

If one unit required provision of more than one signal at a time, therequirement could be satisfied by adding an extra RF processor 485. Forexample, assume that 20 RF processors 485 are provided, and theiroutputs are switched so that they transmit to different ones of the 20units. Assume further that they each produce a single video signalbetween the frequencies of 1-6 Mhz. If one apartment unit requiredtransmission of an additional signal, this could be satisfied byproviding an extra one of RF processors 485, whose output was confinedbetween the frequencies of 6-12 Mhz, and that this output would becombined with the other signal transmitting to the unit in question.

I. Alternative Signal Collection Subsystem 407 b (FIG. 6 b)

Signal collection subsystem 407 b, which represents an alternativeembodiment of signal distribution subsystem 407, is shown in FIG. 6b.This embodiment is simpler and less expensive than subsystem 407 a, yetit allows each local network 411 to transmit a single signal overextended pairs 405 and to have that signal received bytransceiver/switch 400 and applied to communication line 402.

Referring to FIG. 6b, signals from signal separators 413 transmit overpaths 479 to RF converters 486 a-486 c (collectively, RF converters 486)within subsystem 407 b. Because they prepare the individual signalscollected from extended pairs 405 to be combined onto a singleconductive path, RF converters 486 are very similar in function tomodulators 428 of subsystem 407 a. Each RF converter 486 is fixed toshift the energy of its input signal within a particular frequency bandto a different band. As shown in FIG. 6b, this process includes mixingthe input signal with a local oscillator, and filtering of the resultingoutput (e.g., to remove all but one sideband). This process creates anew signal, with identical information content, within the new frequencyband.

The local oscillators used by each of RF converters 486 are such thatthe resulting output frequency bands of the three converters 486 a-486 cdo not overlap. This allows the outputs to be combined onto a singleconductive path. In a preferred embodiment, the frequency bandsconfining the outputs of RF converters 486 are adjacent in addition tonon-overlapping. This minimizes the width of the band occupied by thecombined signals.

The signals produced by RF converters 486 are all transmitted to coupler428′. That component combines the individual signals onto a singleconductive path, and passes it to interface 409, which applies thecombined signal onto communication line 402, as described above.

1) Example #2

Following is an example of communication between transceiver/switch 400and local networks 411 using an embodiment of the communication systemthat includes signal distribution subsystem 403 c, signal collectionsubsystem 407 b, and interface 409 a.

Communication line 402 provides NTSC cable signals at frequenciesbetween 54 Mhz and 850 Mhz. One of the tasks of the communication systemin this example is to make the signals between the frequencies of 300Mhz and 480 Mhz available to local networks 411. Another task is toreceive signals from local networks 411 and to add them to this cablebetween the frequencies of 850 Mhz and 900 Mhz.

The signal from communication line 402 transmits to circulator 421 (FIG.4a) which feeds it to block converter 423 in interface 409. That devicedownshifts the band between 300 to 480 Mhz to the band between 54 to 234Mhz (using an L.O. frequency of 246 Mhz). The result is fed to splitter426′ in subsystem 403 c (FIG. 5c). That component splits the energy ofthe signal five ways, transmitting the signal to RF processors 485 andalso along path 420 b to control signal processor 420.

Using the system, described above, for communication with master control415, users at local network 411 a select a first channel between 60 and66 Mhz, and a second channel between 176 and 182 Mhz. In response,master controller 415 instructs converter 485 a, via link 446 a, toconvert the first channel to an AM signal confined between 1-6 Mhz, andit also instructs converter 485 b to convert the second channel to an AMsignal between 6-12 Mhz. These signals are passed to switch 487.Similarly, users at local network 411 b select a third channel between66 Mhz and 72 Mhz (VHF channel 3) which is converted by RF processor 485c and is provided as an AM signal between the frequencies of 1-6 Mhz.Finally, users at local network 411 c select a fourth channel between182-188 Mhz which is converted by RF processor 485 d to the frequenciesbetween 1-6 Mhz. (A standard 6 Mhz NTSC channel can fit between thefrequencies 1-6 Mhz by filtering out the part of the vestigial sidebandbetween 0-1 Mhz. This is described more fully in the second CIPapplication.)

Each of the signals output by RF processors 485 transmits to switch 487.In response to signals sent by master controller 415 on link 446 c,switch 487 combines the outputs of RF processors 485 a and 485 b andconnects them to path 478 a, thus transmitting these outputs to signalseparator 413 a. Similarly, the output of RF processor 485 c istransmitted over path 478 b to signal separator 413 b, and the output ofRF processor 485 d is transmitted over path 478 c to signal separator413 c. Using techniques described below, signal separators 413 routethese signals to the corresponding ones of extended pairs 405. The fourvideo signals thus transmit local networks 411.

Because the highest frequency transmitted from transceiver/switch 400 tolocal networks 411 is 12 Mhz, in this case, the signals will suffer arelatively small amount of attenuation as they transmit across extendedpairs 405. Thus, there is a relatively high probability that thesesignals will arrive at local networks 411 with energy levels sufficientto be efficiently and clearly transmitted to video receivers 419. It isassumed that such is the case in this example. Thus, video receiver 419a receives one video signal amplitude modulated between 1-6 Mhz, andanother amplitude modulated between 6-12 Mhz. It imparts an upwardsfrequency shift of 60 Mhz to these signals, converting them to thefrequencies between 60-72 Mhz, i.e., VHF channels 3 and 4. This signalis provided to TV 492 a. Similarly, video receivers 419 b and 419 cshift their inputs so that each provides a single signal at VHF channel3 to both TV 492 b and TV 492 c, respectively.

Meanwhile, transmission of signals from local networks 411 totransceiver/switch 400 is also provided. Specifically, video transmitter417 b receives a signal from video camera 494 b, converts it to a single30 Mhz FM video signal between the frequencies of 12-42 Mhz, andtransmits it onto local network 411 b and across extended pair 405 b totransceiver/switch 400. Although it suffers significantly greaterattenuation than the lower frequency video signals transmitting in theopposite direction, its wide bandwidth compensates by allowing thereceiver to tolerate a lower SNR. This signal transmits to signalseparator 413 b. That component directs the signal to RF converter 486 b(FIG. 6b). Video transmitter 417 c feeds a second video signal acrossextended pair 405 c to converter 486 c using a similar process.

Within subsystem 407 b, RF converter 486 b converts its input signal toa 6 Mhz AM signal between 24-30 Mhz, and converter 486 c converts itsinput to a 6 Mhz AM signal between 30-36 Mhz. These signals are passedto coupler 428′ which combines them onto one conductive path andtransmits them to block converter 447 in interface 409 (FIG. 4a). Blockconverter 447 them shifts these signals upwards to the frequency bandspanning 850-862 Mhz. Block converter 447 then amplifies the shiftedsignal, and passes it through circulator 421 b and onto communicationline 402. Once on that medium, these two signals transmit in theopposite direction of the 30 NTSC signals that transmit between 300-480Mhz.

J. Transmission and Recovery of Signals from a Single Twisted Pair in aBundle (FIGS. 9 a-9 b)

A primary purpose of signal separators 413 is to receive signals fromprocessor 418 and apply them to extended pairs 405 while simultaneouslyreceiving signals from extended pairs 405 and transmitting them toprocessor 418 and to control signal processor 420. To perform thisfunction, each signal separator 413 is connected between an extendedpair 405 and the corresponding one of twisted pairs 476.

The remaining part of the description of signal separators 413 will becast in terms of signal separator 413 b and local network 411 b. Twoembodiments of signal separators 413 will be described. One embodiment,shown in FIG. 9a and described first, is appropriate when telephonesignals transmit over extended pairs 405 in the ordinary manner, i.e.,at voiceband frequencies. The other embodiment is appropriate whentelephone signals transmit over extended pairs 405 at frequencies abovevoiceband, as depicted in FIG. 3b. This embodiment is shown in FIG. 9b.

Referring to FIG. 9a, signals that are applied to signal separator 413 bare converted and routed in the following manner:

1) Telephone signals from local exchange 475 transmit across extendedpair 476 b and through filter 474 b, entering the “exchange” port ofseparator 413 b. These signals are applied directly to the “local” portand exit the “local” port unchanged.

2) Telephone signals from local network 411 b transmit across extendedpair 405 b, presenting at the “local” port. These signals exit the“network” port, also unchanged.

3) Signals recovered from communication line 402 that are processed byprocessor 418 and output by switch 401 (FIG. 5a) transmit across path478 b to the “distribution” port of signal separator 413 b. Thesesignals exit the “local” port.

4) Infrared control signals detected by video receiver 419 b and fedonto local network 411 b and transmitted (after reception, processingand retransmission by local network interface 404 b, if 404 b isprovided) across extended pair 405 b are applied to the “local” port.These signals are targeted for master controller 415, and are routedthrough the “control” port and along path 477 b to filter 427 b incontrol signal processor 420 (FIG. 7). These signals also transmitthrough the “collection” port and along path 479 b, but are ignored bysignal selection subsystem 403.

5) Video signals fed by video transmitter 417 b onto local network 411 btransmit (after reception, processing and retransmission by localnetwork interface 404 b, if 404 b is provided) across extended pair 405b to the “local” port. These signals are routed through the “collection”port and transmit across path 479 b to amplifier 408 b. (Similarly,digital signals fed by transceiver 491 c onto local network 411 ctransmit across extended pair 405 c and are routed to amplifier 408 c.)These signals also transmit through the “control” port and along path477 b to filter 427 b in control signal processor 420. Those signals areblocked from further transmission, however, by filter 427 b.

In the embodiment shown in FIG. 9a, signals transmitting throughseparator 413 b are not processed, i.e. they are not amplified, orconverted in frequency or waveform.

The major components of signal separator 413 b are high pass filter 451,coupling network 459, splitter 458, and invertor 496. These componentsprovide the signal routing and processing described above. It will beappreciated that other embodiments of signal separator 413 b thatachieve the signal routing and signal conversion described above arealso possible.

Transmission of telephone signals through signal separator 413 b isstraightforward. A simple conductive path connects between the “local”port and the “exchange” port, thereby connecting low pass filter 474 bon twisted pair 476 b with extended pair 405 b. Because low pass filter474 b passes all voiceband energy, this connection completes an simpleunbroken conductive path between local exchange 475 and local networkinterface 404 b. High pass filter 451 prevents any telephone signalsfrom diverting towards coupling network 459.

Low pass filters 474 block transmission of the high frequency signalstransmitting through signal separators 413 between processor 418 andlocal network interfaces 411. In addition to preventing the “splittingloss” of these high frequency signals, filters 474 prevent them fromcreating violations of governmental regulations by conducting onto thepublic telephone network. Part 68 of the FCC regulations in the U.S.,for example, severely limits the energy that can be conducted onto thepublic network by signals above voiceband and below 6 Mhz.

Video and other non-telephone signals transmitting over extended pair405 b from local network 411 b transmit through the “local” port. Thesesignals pass through high pass filter 451 to coupling network 459. Theyare blocked from transmitting towards local exchange 475 by low passfilter 474 b (FIG. 2).

At coupling network 459, directional coupling directs signals receivedfrom extended pair 405 b to splitter 458, isolating these signals fromtransmitting through invertor 496 (which is described below) to path 478b leading to subsystem 403. Reverse isolation in invertor 496 can alsoblock these signals from path 478 b. If this isolation is not provided,these signals may transmit through switch 401 to the output ofmodulators 410, where they will be blocked by the reverse isolation ofthose components. (If subsystem 403 follows the embodiment shown in FIG.5c, reverse isolation will be provided by RF processors 485.)

The energy of the non-telephone signals is divided by splitter 458, sothe signals transmit across path 477 b to control signal processor 420and across path 479 b to signal collection subsystem 407. An amplifier,(not shown) can be provided internal to splitter 458 to compensate forthe 3 dB of energy lost during splitting.

Control signals targeted for master controller 415 that transmit acrosspath 477 b continue through filter 427 b (FIG. 7) in control signalprocessor 420 to demodulator 443 b. (All signals at the frequenciescovered by the passband of filter 427 b are considered to be intendedfor communication with master controller 415.) Processing of thesesignals internal to processor 420 is described below. Other signals,such as video signals, transmitting along path 477 b will be blocked byfilter 427 b.

Signals transmitting across paths 479 b to subsystem 407 a (FIG. 6a)transmit to amplifier 408 b. These signals are amplified and transmittedthrough switch 429 to one or more demodulators 416. Video signals andsignals other than the control signals intended for communication withmaster controller 415 are then subject to selection by demodulators 416,as described above. Signals not selected terminate at that point. Ifsubsystem 407 b is provided in place of subsystem 407 a, the same typeof signal selection takes place at RF converter 486 b.

Signals received by processor 418 from communication line 402 that areprocessed by processor 418 and output by switch 401 (FIG. 5a) transmitacross path 478 b to the “distribution” port of signal separator 413 b.These signals transmit through invertor 496 to coupling network 459.Directional coupling internal to coupling network 459 directs thesesignals to high pass filter 451, while isolating them from transmittingto splitter 458. The signals from processor 418 emerge from filter 451and transmit onto extended pair 405 b.

Invertor 496 is supplied to reduce the possibility, described above, ofincreased crosstalk interference when the same video signal transmitswithin the same frequency band to multiple local networks 411. Thispossibility is reduced as follows. Invertor 496, which is an ordinaryand inexpensive electronic component, implements a 180 degree phaseshift across all frequencies. This phase shift is accomplished by simplyconverting negative voltages to positive, and vice versa. Thus, thepolarity of the output of invertor 496 is the opposite of that of itsinput, and by placing an invertor 496 as shown in FIG. 9a inapproximately half of signal separators 413, the likelihood that theelectric fields created by each of the pairs in the group of extendedpairs 405 will cancel each other is increased. A component thatimplements a slight delay in transmission can produce a similar affectif the delay times are slightly different for each of signal separators413. Both methods tend to prevent the interference from addingcoherently.

In addition to providing directional multiplexing, coupling network 459also balances the signals transmitting towards filter 451, and matchesthe impedance of the conductive path internal to signal separator 413with the impedance of extended pair 405 b. This tends to reduce theradiation of these signals and improve the efficiency of the transfer ofenergy between pairs 405 and signal separators 413.

Balancing and impedance matching circuitry are shown in FIGS. 6 and 7 ofthe parent application, for a coupling network that served as a junctionof three paths. Those skilled in the art can convert the wound-torroiddescribed therein to achieve the balancing and impedance matchingresults for this case.

If directional multiplexing in coupling network 459 is not sufficient toprevent transmission of signals from subsystem 403 from transmitting tosplitter 458, filtering internal to splitter 458 can prevent thesesignals from exiting the splitter onto paths 477 b or 479 b. This typeof filtering is possible because, as described above, the frequenciesused by signals transmitting towards local networks 411 are differentfrom the frequencies used by signals transmitting towardstransceiver/switch 400.

1) Example #3

Referring also to FIG. 8, the routing of each of the signals used in theprevious example is now described. Signals communicating with localnetwork 411 a are routed by signal separator 413 a, those communicatingwith local network 411 b are routed by signal separator 413 b, and thosecommunicating with local network 411 c are routed by signal separator413 c.

Video signal U and video signal V exit switch 401 on conductive path 478a. Video signal U is confined within the 1-6 Mhz band, as shown in FIG.3a, and video signal V is confined between 7-22 Mhz. These signalstransmit along path 478 a to signal separator 413 a, transmittingthrough invertor 496 to coupling network 459. They continue on throughhigh pass filter 451 and onto extended pair 405 a.

Simultaneously, video signal V exits switch 401 along path 478 b atfrequencies between 1-6 Mhz. Signal V transmits to signal separator 413b, transmitting through invertor 496 to coupling network 459. Itcontinues on through high pass filter 451 and onto extended pair 405 b.Video signal V follows a similar path at similar frequencies, exitingswitch 401 along path 478 c to signal separator 413 c, and transmittingonto extended pair 405 c.

Meanwhile, digital signal Y exits switch 401 confined between thefrequencies of 6-18 Mhz. It follows a path to extended pair 405 c usingthe same route as video signal V.

Video signals W and X, digital signal Z, and control signals A, B, and Call transmit in the reverse direction. Video signal W and control signalB are both transmitted onto local network 411 b. These signals areintercepted by local interface processor 404 b and retransmitted acrossextended pair 405 b to signal separator 413 b. Inside that signalseparator 413 b, video signal W and control signal B pass through highpass filter 451 to coupling network 459. These signals are directed bythat network towards splitter 458. That component splits the signalenergy, transmitting half along path 477 b to filter 427 b in processor420 and half along 479 b to splitter 408 b in processor 418. Filter 427b allows only control signal B to pass through to be processed bycontrol signal processor 420. (Ultimately, control signal B willcommunicate with master controller 415.) Video signal W and controlsignal B both pass along path 479 b to amplifier 408 b in collectionsubsystem 407 a, and exit to switch 429. Only video signal W, however,is transmitted by switch 429 to demodulators 416.

Video signal X, control signal C, and digital signal Z, meanwhile, areapplied to local network 411 c and transmit across extended pair 405 cto signal separator 413 c. The filtering and directional multiplexinginternal to that component directs them through splitter 458 and acrosspath 479 c to amplifier 408 c. The signals input to splitter 408 c alsotransmit across path 477 c to filter 427 c in signal processor 420.

Finally, control signal A transmits across extended pair 405 a to signalseparator 413 a which directs it to filter 427 a in control processor420 and to amplifier 408 a in subsystem 407 a.

2) Transmitting Telephone Signals Above Voiceband (FIG. 9b)

The embodiment of signal separator 413 b shown in FIG. 9b is nowdescribed. This embodiment is used when signals received fromcommunication line 402 are transmitted by transceiver/switch 400 acrossextended pair 405 b using, in addition to higher frequencies,frequencies at voiceband. (The spectral distribution of these signals isshown in FIG. 3b.) As described above, signal separator 413 b and localnetwork interface 404 b cooperate, in this embodiment, to transmittelephone signals at frequencies above voiceband.

Referring to FIG. 9b, the major components of signal separator 413 b arecoupling network 422, telephone signal processor 424, and impedancematcher 480. Processor 424 works in conjunction with local interface 404b to communicate telephone signals across extended pair 405 b at RFfrequencies.

Telephone signals from local exchange 475 transmit at voiceband throughlow pass filter 474 b (FIG. 2) and through the “exchange” port ofseparator 413 b to conversion circuitry 464, which is part of processor424. Circuitry 464 converts all of these signals to RF frequencies. Theconverted signals include voice, ringing, and hookswitch signals. Theconverted telephone signals are transmitted through bandpass filter 425to coupling network 422.

Filter 425 passes energy within the bands occupied by the telephonesignals in their RF form, but blocks all other signals, includingvoiceband signals. This prevents conversion circuitry 464 from loadingdown non-telephone signals that transmit to processor 424.

The telephone signals transmitted from local exchange 475 always exitthe “local” port of signal separator 413 b because filters located onthe paths exiting network 422 block these signals from exiting throughthe “collection,” “distribution,” and “control” ports. (This filteringis described below.) These signals transmit onto extended pair 405 b.They are received and converted back to their original form by localnetwork interface 404 b as will be described below. The reconvertedsignals are then transmitted onto local network 411 b as normalvoiceband signals.

Telephone signals transmitting in the reverse direction, from telephonedevice 414 b to local exchange 475, are converted in the followingmanner. Local network interface 404 b intercepts the signals fromtelephone device 414 b, which are at voiceband, converts them to RFsignals, and transmits them across extended pair 405 b. Processing oftelephone signals by local network interfaces 404 is described ingreater detail below.

Telephone signals in the RF band from extended pair 405 b transmitthrough the “local” port of signal separator 413 b to coupling network422. These signals then transmit to telephone signal processor 424 butare blocked from exiting network 422 towards the “collection,”“distribution,” and “control” ports by filters connected to the pathsleading to those ports. (Coupling network 422 is described in greaterdetail below.) These telephone signals pass through filter 425 toconversion circuitry 464 which converts them back to voiceband, andtransmits them to filter 474 b and across twisted pair 476 b to localexchange 475.

Means to convert telephone signals from voiceband to RF signals and backto voiceband are well known and can be used to implement the functionsof conversion circuitry 464 and the companion conversion component inlocal network interfaces 404. Indeed, common cellular or cordlesstelephones convert voiceband, switchhook, and ringing signals to RFfrequencies to transmit the signals over a wireless link to a telephoniccommunication line.

Routing of non-telephone signals through signal separator 413 b (asshown in FIG. 9b) is now described. Coupling network 422 includesdirectional couplers 466 and 467 and splitter 468. Couplers 467 and 466each have a joined port and left and right isolated ports. Signalspresenting at a joined port pass to through to each of the isolatedports. (The signal energy is evenly split.) Signals presenting at anisolated port exit through the joined port, but are blocked, (e.g. havea 30 dB loss) from exiting the other isolated port.

Signals from extended pair 405 b pass through the “local” port andpresent at impedance matcher 480. These signals include both telephonesignals, control signals, and signals destined for transmission tocommunication line 402. Impedance matcher 480 matches the impedance ofthe telephone line to the circuitry internal to transceiver/switch 400.

After passing through impedance matcher 480 these signals transmit todirectional coupler 467, exiting through both of the isolated ports andtransmitting to the joined port of coupler 466 and splitter 468. Signalspresenting at the joined port of coupler 466 exit both of the isolatedports. As can be seen by tracing the paths, signals exiting the isolatedport leading towards switch 401 in subsystem 403 (i.e., the rightisolated port of coupler 466) pass through to modulator 410 b where theyare blocked (i.e. meet a high impedance) by the reverse isolation at theoutput of that device. A filter can be provided at the output ofmodulator 410 b to prevent loading down of these signals.

From among the signals that pass out the left isolated port of coupler466 leading towards processor 424, only telephone signals are receivedby processor 424. These are processed as described above. Non-telephonesignals are blocked by filter 425 in that processor.

Signals from extended pair 405 b that present at the joined port ofcoupler 467 and exit the left isolated port towards splitter 468 aresplit and routed to filter 427 b in control signal processor 420 andamplifier 408 b in subsystem 407 of processor 418. As will be describedlater on, filter 427 b blocks signals other than those at frequenciesused by the control signals that communicate with master controller 415.Thus, processor 420 separates the special control signals from the groupof “collected” signals.

As described above, signals presenting at amplifier 408 b are amplifiedand transmitted through switch 429 to demodulators 416. Video signalsand signals other than telephone signals and control signals intendedfor communication with master controller 415 are then subject toselection by demodulators 416, as described above. Signals not selectedterminate at that point. (Thus, control signals and telephone signalswill terminate.) If subsystem 407 b is provided in place of subsystem407 a, the same type of signal selection takes place at RF converters486.

As described above, the signals received by processor 418 fromcommunication line 402 that are intended for transmission to localnetwork 411 b are output from switch 401 (in subsystem 403 a, FIG. 5a).These signals exit along path 478 b, pass through the distribution portof signal separator 413 b and through invertor 496 to the right isolatedport on directional coupler 466 in coupling network 422 (This path canbe traced in FIGS. 2 and 9b.)

Signals passing through the right isolated port of directional coupler466 exit through the joined port of coupler 466. (They are substantiallyblocked from exiting the left isolated port by the directionalmultiplexing of coupler 466; filter 425 blocks the portion of the energythat exits from the left isolated port.) They then pass through the leftisolated port of coupler 467, to the joined port of coupler 467. (Theyare blocked from exiting the other isolated port of coupler 467 by thedirectional multiplexing and, ultimately, by the reverse isolation ofmodulators 410.) Finally, they pass though the joined port of coupler467, through impedance matcher 480 b onto extended pair 405 b. Theimpedance matching enables these signals to feed onto extended pair 405b, which has a different impedance, without substantial signalrefections.

K. Signal Processing at the Local Network Interface (FIGS. 10-13)

The signals fed to one of extended pairs 405 by transceiver/switch 400are received at the opposite end by the corresponding one of localnetwork interfaces 404 which processes these signals and retransmitsthem onto the corresponding one of local networks 411. If two-waycommunication between transceiver/switch 400 and local networks 411 isperformed, each local network interface 404 also receives signalstransmitted onto local networks 411 and transmits them onto thecorresponding one of extended pairs 405.

The primary function of local network interfaces 404 is to process thesignals intercepted from extended pairs 405 so that when they areretransmitted their ability to communicate to the RF receivers connectedto local networks 411 will be enhanced. Processing of signalstransmitting towards transceiver/switch 400 provides similar benefits.

A particularly important process performed by local network interfaces404 is amplification. This allows signals transmitting along thetransmission path between transceiver/switch 400 and the RF receivers onlocal networks 411 to be amplified at an intermediate point, boostingtheir energy levels up to the maximum limit (i.e., the limit at whichthey radiate RF energy just below governmental limits.) Thisre-amplification will improve the SNR at the receive end, increasing theattenuation that the signal can encounter along the transmission pathwhile still being successfully received. Processing that converts signalwaveform and frequency can also be useful, as described below.

In some embodiments, particularly those where a video signal istransmitted over one of extended pairs 405 at baseband frequencies (FIG.3B), telephone signals transmit from transceiver/switch 400 to localnetwork interfaces 404 at RF frequencies, having been converted fromvoiceband by a telephone signal processor 424 in one of signalseparators 413. When telephone signals transmit at RF frequencies, localnetwork interfaces 404 convert the signals received from extended pairs405 to ordinary voiceband telephone signals, and feed them onto thecorresponding local networks 411 for reception by telephone devices 414in the ordinary manner. Conversion also takes place in the oppositedirection. I.e., voiceband telephone signals from devices 414 thattransmit across local networks 411 are received by the correspondinglocal network interfaces 404, frequency converted, and applied to thecorresponding one of extended pairs 405 at RF frequencies.

A general embodiment of a local network interface 404 is shown in FIG.10. The description that follows will be cast in terms of local networkinterface 404 b, but applies, of course, to any one of local networkinterfaces 404 shown in FIG. 1a.

Referring to FIG. 10, the principle components of local networkinterface 404 b are the telephone signal processing section 470, generalsignal processing section 471, coupling networks 437 and 449, and highpass filter 463. All signals from extended pair 405 b transmit tocoupling network 437, and high-frequency (i.e., non-voiceband) signalsfrom local network 411 b transmit through high pass filter 463 tocoupling network 449. Directional multiplexing and filtering in couplingnetworks 437 and 449, and filtering on paths connected to these couplingnetworks, cause the converging signals to be routed as follows.Telephone signals from extended pair 405 b are blocked by filters 438,445 in general signal processing section 471 and thus are routed throughtelephone signal processing section 470 and onto local network 411 b(and are blocked from coupling network 449 by high pass filter 463).Telephone signals also transmit across the same path in the oppositedirection. Non-telephone signals from extended pair 405 b are routed togeneral processing section 471, and non-telephone signals from section471 pass through coupling network 437 to extended pair 405 b. Also,non-telephone signals from local network 411 b transmit to generalprocessing section 471, and non-telephone signals from generalprocessing section 471 transmit onto network 411 b.

The transmission of telephone signals through local interface 404 b andthe details of telephone signal processing section 470 are describedfirst. That description also includes a description of two particularembodiments of coupling network 437. Several embodiments of generalprocessing section 471 and coupling network 449 are described afterthat.

1) Transmission of Telephone Signals across Local Interface 404 b (FIGS.13a, 13 b)

When non-telephone signals transmitting on extended pair 405 b do nothave energy at voiceband frequencies, (e.g. the video signalsrepresented in FIG. 3a or 3 c) signal separators 413 according to FIG.9a are used, and the telephone signals communicating between localexchange 475 and telephone devices 414 b are confined to the voiceband.FIG. 13a shows coupling network 437 a which is an embodiment of network437 used when telephone processor 424 is not included in signalseparator 413 b. In this case, the telephone signals are at voiceband.

Referring to FIG. 13a, voiceband telephone signals from extended pair405 b that transmit to interface 404 b are blocked by high pass filter472 in coupling network 437 a, passing instead through low pass filter442, which is designed to pass only energy at voiceband frequencies, intelephone signal processing section 470 a. These signals continue on tolocal network 411 b. (They are blocked from the alternative path by highpass filter 463.) Transmission of telephone signals in the oppositedirection traces the reverse path. Thus, an unbroken path for voicebandsignals from telephone device 414 b (FIG. 1a) to local exchange 475 isprovided.

FIG. 13b shows coupling network 437 b and telephone signal processingsection 470 b, which are specific embodiments of network 437 and section470. Section 470 b processes telephone signals that transmit overextended pair 405 b at frequencies above voiceband (e.g., at RF).

All signals from extended pair 405 b are applied directly to coupler 437b. Coupler 437 b matches the impedance of each of the five paths thatconverge at its ports. Coupler 437 b also balances the signalstransmitting from interface 404 b onto extended pair 405 b. Finally,coupler 437 b allows all converging signals to flow through freely tothe other ports, meaning that routing of signals through that coupler isdetermined by the surrounding filters. (An example of such a coupler isshown in the first CIP application.)

Telephone signals transmitting over extended pair 405 b at frequenciesabove voiceband that transmit to coupler 437 b are routed to band passfilter 454 and are blocked on all other exiting paths by filters thatpass different frequency bands. The signals passed by filter 454continue on to telephone signal converter 452. Converter 452 convertsthese signals to voiceband and transmits them through low pass filter455 to local network 411 b where they communicate with telephone device414 b in the ordinary manner. High pass filter 463 blocks these signalsfrom transmitting along the alternative path.

In the reverse direction, processor 452 receives telephone signals atvoiceband from local network 411 b via low pass filter 455. Processor452 converts these signals to RF and passes them through filter 453 tocoupler 437 b. These signals transmit only onto extended pair 405 bbecause they are blocked from the other paths (by filters 445, 438, and454). This completes a two-way telephone communication link using RFbetween processor 452 and telephone signal processor 424 in signalseparator 413 b at transceiver/switch 400.

2) Transmission of Non-Telephone Signals from Extended Pair 405 b toLocal Network 411 b

Referring again to FIG. 13a, non-telephone signals from extended pair405 b that transmit to coupling network 437 a pass through high passfilter 472 to coupler 483. They are blocked from the alternative path byfilter 442, which passes only voiceband signals.

Coupler 483 matches the impedance of each of the three paths thatconverge at its ports. Coupler 483 also balances the signalstransmitting from interface 404 b onto extended pair 405 b.

In one embodiment of coupler 483, all signals converging at its portsflow freely through to the other ports. This means that the routing ofsignals through couplers 483 is determined by the filters on theconnecting paths. In an alternative embodiment of coupler 483, isolationis provided between the two paths leading to local processor 439 (FIG.10). This increases the separation provided at coupling network 483 byfilters 445 and 438.

Referring to FIG. 13b, coupler 437 b matches the impedance of each ofthe paths that converge at its ports and balances the signalstransmitting from interface 404 b onto extended pair 405 b. All signalsconverging at coupler 437 b pass freely out the other ports, meaningthat routing of signals through coupler 437 b is determined by thefilters connected to its ports.

Non-telephone signals received from pair 405 b that transmit to coupler483 (in FIG. 13a) or coupler 437 b (in FIG. 13b) exit on the pathleading to filter 438 (FIG. 10). Filter 438 passes only energy atfrequencies used by non-telephone signals transmitted bytransceiver/switch 400, allowing those signals to pass through to localprocessor 439. The same signals are blocked along the path leading fromnetwork 437 by filter 445, which passes only energy at frequencies usedby non-telephone signals transmitting towards transceiver/switch 400.(In FIG. 13b, non-telephone signals received from extended pair 405 bare also blocked from the two other paths by filters 453 and 454.) Thus,all non-telephone signals received from extended pair 405 b are receivedby local processor 439.

After processing, local processor 439 transmits these signals to filter460, and they ultimately transmit onto local network 411 b, as will bedescribed below. To avoid interference with telephone communication onlocal network 411 b, signals transmitted by processor 439 to filter 460are always provided at frequencies above the ordinary telephonevoiceband.

One important function of processor 439 (and of local network interfaces404) is to amplify non-telephone signals received from filter 438,relaying them onto local network 411 b at a higher energy level, therebyincreasing the SNR at the input to the RF receivers connected to localnetworks 411. Without this increase, the attenuation in transmittingfrom transceiver/switch 400 may prevent signals from reaching thereceive end with sufficient SNR.

Another function of processor 439 is to convert signals from filter 438to the waveform (i.e., the modulation method) and frequency at whichthey will transmit onto local network 411 b. Changing the waveform andfrequency can simplify the design of the RF receivers of these signals,e.g., video receivers 419 and transceiver 491 c. This is especially trueif video is transmitted over pair 405 b in FM form, or if the videosignals transmitted by interface 404 b onto local network 411 b mustcoordinate with video signals transmitting locally, e.g., from videotransmitters 417 b to video receiver 419 b. (Choosing waveforms forvarious video signals transmitting across a local network and arrangingtheir frequency bands to simplify receiver design is thoroughlydiscussed in the second CIP application.) Various embodiments ofprocessor 439, some of which perform frequency and waveform conversion,all of which perform amplification, are given below.

Additional details of the routing of signals transmitting from processor439 to local network 411 b are now described. Filter 460 blocks energyat all frequencies except those used by signals fed to that filter fromprocessor 439. The signals passed by filter 460 transmit to couplingnetwork 449.

Coupling network 449 serves as a junction for signals converging fromthree paths. Signals flow freely through this junction, exiting each ofthe opposite two paths. Thus, filters 460, 461, and 463 determine therouting of the signals at coupling network 449.

Signals transmitting to coupling network 449 from filter 460 exitthrough the port leading to high pass filter 463. That filter blocksonly voiceband signals, allowing the signals from processor 439 to passthrough onto local network 411 b. Filter 455 in telephone signalprocessor section 470 b (FIG. 13b) blocks signals from processor 439from transmitting along the alternative path. Filter 442 in telephonesignal processor section 470 a (FIG. 13a) performs a similar function.Because it is a low-pass filter, filter 442 also suppresses the energyof transients and harmonics of voiceband signals originating attelephone device 414 b (or other telephone devices connected to localnetwork 411 b) from transmitting onto extended pair 405 b. Because thesemay contain significant energy at higher frequencies, they canordinarily cause interference with the RF signals communicating overthat pair. The low pass filters that connect between devices 414 and thelocal networks 411 can also suppress these harmonics.

In addition to serving as a junction, coupling network 449 matches theimpedance of the wiring of local network 411 b to the circuitry internalto interface 404 b. It also balances RF signals flowing from processor439 onto local network 411 b, and unbalances RF signals flowing in theopposite direction. These functions tend to minimize radiation andincrease the efficiency of the transfer of RF energy between localnetwork 411 b and interface 404 b.

Referring also to FIG. 8, the following example shows how signals fromextended pair 405 a are coupled by local network interface 404 a ontolocal network 411 a. Video signals U and V are fed onto extended pair405 a by signal separator 413 a in transceiver/switch 400. Signal U isamplitude modulated in the 1-6 Mhz band, while signal V is frequencymodulated in the 7 to 22 Mhz range. At local network interface 404 a,these signals transmit to network 437, and exit towards filter 438.(They are blocked from the other paths by the surrounding filters.)Signals U and V pass through filter 438 and are received by processor439.

Processor 439 demodulates video signal V, and remodulates it using AMbetween the frequencies 24-30 Mhz at a signal level of 40 dB mV. Inparallel with this process, processor 439 demodulates video signal U andremodulates it using AM between the frequencies 12-18 Mhz and at asignal level of 40 dB mV. These signals are combined onto a singleconductive path and fed through filter 460 to coupling network 449. Theypass through that network, exiting through filter 463 and onto localnetwork 411 a. Video receiver 419 a recovers these signals from thenetwork, and block converts them upwards by 164 Mhz, providing them totelevision 492 a at 176-182 Mhz (VHF channel 7) and 188-194 Mhz (VHFchannel 9). (A design for a video receiver that performs such aconversion is given in the second CIP application.) One of the detailedembodiments of processor 439 shown below includes import processor 440b. That component is designed to conduct the processing required toperform the conversion of video signal U and video signal V used in thisexample.

3) Transmission of Non-Telephone Signals from Local Network 411 b toExtended Pair 405 b

Video transmitter 417 b connects to local network 411 b to transmitsignals at frequencies above voiceband. Examples of these signals areordinary video signals from video cameras, digital signals fromcomputers, and control signals from infrared transmitters. These signalsare referred to as non-telephone signals because they are not meant tocommunicate to local exchange 475. Techniques that transmit thesesignals across networks such as local network 411 b are described in theparent and first and second CIP applications.

Certain control signals transmitted by video receiver 419 b are intendedto communicate with master controller 415 in transceiver/switch 400.These signals indicate, among other things, which signals are to berecovered from communication line 402 and transmitted over extended pair405 b to local network 411 b. Master controller 415 can make thesedeterminations because it controls certain other components intransceiver/switch 400, as described above.

Because many potential users are familiar with issuing control signalsusing infrared transmitters, that is the preferred method of originatingthese control signals, e.g., issuing infrared signals from remotecontrol transmitter 493 b. Video receivers 419 b detect these infraredpatterns and convert them to voltage variations that are applied tolocal network 411 b and received by local network interface 404 b. Thatcomponent relays the control signals across extended pair 405 b totransceiver/switch 400 where it is received, as described above, bycontrol signal processor 420.

Referring to FIG. 10, non-telephone signals fed to local network 411 bfor transmission to transceiver/switch 400, are blocked by a highimpedance at telephone signal processing section 470. (In the embodimentof section 470 b, this impedance is supplied by low pass filter 455. Inthe embodiment of section 470 a, this impedance is supplied by low passfilter 442.) Because these signals are expressed in RF, however, theypass through high pass filter 463 to coupling network 449. These signalswill exit that network towards filter 461, but will be blocked from theother exit by filter 460. (As described above, filter 460 only allowsenergy used by signals transmitting from processor 439 to pass.) Thus,signals from video transmitter 417 b will pass through filter 461 toprocessor 439.

Among the signals received from filter 461, those intended fortransmission to communication line 402 are converted by processor 439 tothe waveform, frequency, and amplitude at which they will be fed toextended pair 405 b. The relationship between these characteristics andthe reliability of communication over extended pair 405 b was describedabove. Processor 439 feeds the converted signals through filter 445. Thesignals are then forced by the filtering (i.e., blocked by filters 438and 442) though coupling network 437 and onto the corresponding extendedpair 405 b.

In some embodiments, signals recovered by processor 439 from localnetwork 411 b are processed and retransmitted onto that network. Such aprocedure, and its attendant advantages, is described in the second CIPapplication. That procedure is included as an option of thecommunication system described herein because local network interfaces404 provide a natural place to implement such a retransmission process.A specific embodiment of processor 439 that retransmits signals backonto local network 411 b is described below.

Referring also to FIG. 8, the following is an example of transmission ofsignals from local network 411 b through processor 439 to extended pair405 b. Video transmitter 417 b receives video signal W at baseband fromvideo camera 494 b, amplitude modulates it between 6-12 Mhz, and feedsit onto local network 411 b where it transmits to filter 463 in localnetwork interface 404 b. Being blocked by low pass filter 455 (or byfilter 442 when the embodiment shown in FIG. 13a applies) and filter460, signal W transmits through high pass filter 463, coupling network449 and filter 461 to processor 439. Processor 439 converts video signalW to an FM signal between 24-54 Mhz, and transmits it through filter 445and coupling network 437 onto extended pair 405 b. (The relatively widebandwidth is advantageous because, being at relatively high frequencies,the signal will suffer more attenuation and be received at a lower SNR.Increasing the bandwidth compensates for this by making the receptionprocess more sensitive.)

Meanwhile, video receiver 419 b detects control signal B (FIG. 8) whichis issued by the user with infrared remote control transmitter 493 b.Video receiver 419 b converts this signal to voltage variations withinthe 0.5 Mhz band centered at 23 Mhz, and feeds the signal onto localnetwork 411 b. Following the same route as video signal W, controlsignal B transmits to processor 439. Processor 439 receives controlsignal B and video signal W combined on the same conductive path. Afterprocessing, control signal B is at a higher energy level. (Signal W isconverted as described above.) The two signals are fed through filter445 to coupling network 437. Filtering at network 437 routes thecombined signal onto extended pair 405 b. One of the detailedembodiments of processor 439 shown below includes export processor 441b. That component is designed to conduct the processing of video signalW and control signal B used in this example.

It will be appreciated that the part of signal processor 439 thatreceives RF signals from pair 405 b and the part that feeds signals ontopair 405 b, together with coupling network 437 and filters 438, 445, and442 comprise a transceiver that performs two-way RF communication with anetwork of active twisted pair wiring, specifically, extended pair 405b. A complete description of the basic signal processing elementsrequired of such a transceiver is given in the first CIP application.The processing implemented by components 439, 437, 445, 442, and 438 ofthis disclosure includes those elements.

It will further be appreciated that the part of signal processor 439that receives RF signals from local network 411 b and the part thatfeeds signals onto local network 411 b, together with coupling network449 and filters 442, 460, 461, and 463 also comprise a transceiver thatperforms two-way RF communication with a network of active twisted pairwiring, specifically, local network 411 b. A complete description of thebasic signal processing elements required of such a transceiver is alsogiven in the first application. The processing implemented by components449, 460, 442, 461, 463, and 439 of this disclosure includes thoseelements.

4) Details of Specific Embodiments of Local Processor 439 (FIGS. 11a, 11b)

FIG. 11a shows processor 439 a which is a specific embodiment ofprocessor 439. In processor 439 a, all of the non-telephone signalsreceived from local network 411 b are transmitted through filter 445 andonto extended pair 405 b, and all non-telephone signals received by thatprocessor from extended pair 405 b are transmitted through filter 460and onto local network 411. This simplifies the design, enablingprocessor 439 a to be separated into two independent processors. As isseen in FIG. 11a, non-telephone signals transmitting from extended pair405 b onto local network 411 b transmit through import processor 440.Non-telephone signals transmitting in the other direction, from localnetwork 411 b to extended pair 405 b, transmit through export processor441.

Import processor 440 converts the signals it receives from extended pair405 b to the waveform, frequency, and signal level at which they are fedthrough filter 460, network 449, and high pass filter 463 onto localnetwork 411 b. FIG. 11b shows three different embodiments of importprocessor 440.

Processor 440 a, which is shown at the top of FIG. 11b, does not alterthe waveform or frequency of its input. Rather, processor 440 a simplyadjusts the signal energy to a selected level. Typically, thisadjustment results in an amplitude increase, thereby increasing the SNRat the RF receivers connected to local network 411 b.

Typical governmental regulations do not limit the total energy that canbe radiated by a single device. Rather, each individual signaltransmitted by an RF device faces limitations on the radiation it cangenerate. For this reason, transceiver/switch 400 feeds each signal toextended pairs 405 at energy levels that create radiation just below thelegal limits. This will maximize the SNR at the opposite end of extendedpairs 405. For the same reason, import processor 440 a boosts the levelsof the signals it receives back to these “maximums” beforeretransmission onto local network 411 b.

Because signals at higher frequencies encounter more attenuation, theywill be received at levels further below the maximum than lowerfrequency signals. Thus, import processor 440 a provides a gain thatincreases with frequency. This is achieved by a two phase process. Inthe first phase, the same gain is imparted to signals at all frequenciesby amplifier 499. In the second phase, filter 497 applies an attenuationto the signal that decreases with increasing frequency, thus providingan output signal whose gain increases with frequency. Although thistwo-phase process is described herein, other techniques that impart a“sloped gain” can be used.

To provide a device that can be used in a variety of installations,processor 440 a allows the overall gain and the slope of the gain to beadjusted. As shown in FIG. 11b, these adjustments are preferably manual.(Alternatively, the adjustments can be made automatically using suitablefeedback techniques.) Manual means are acceptable because the levels ofsignals received from transceiver/switch 400 are not likely to change,making an initial adjustment sufficient. Also, it is likely that localnetwork interfaces 404 will be professionally installed, removinganother reason for providing automatic adjustment.

Processor 440 b (shown in the center of FIG. 11b) is designed to receivemultiple (two in the embodiment shown) signals from extended pair 405 c.(Because they are recovered from a single pair, of course, each signalwill be confined within different frequency bands.) Processor 440 bdemodulates, basebands and then remodulates each signal, providing themat a specific waveform, frequency, and energy level.

Processor 440 b is especially useful when the signals transmitted overpairs 405 are FM video signals. If video signals transmit onto localnetworks 411 in FM form, video receivers 419 must convert them to AMbecause most ordinary televisions only receive AM signals. (Some receiveunmodulated signals, none receive FM video signals.) Referring to FIG.8, processor 440 b can implement the conversion that local networkinterface 404 a performs on video signals U and V before those signalsare transmitted onto local network 411 a.

The functioning of processor 440 b is as follows. The combined signalsare divided in power by splitter 430, transmitting to demodulators 431 aand 431 b. Each of those components basebands a different one of thesignals. The basebanded signals transmit to modulator/amps 432 a and 432b, respectively. These components convert their basebanded signal to thenew waveform, frequency band, and energy level, and feed them to coupler433. (FIG. 11b shows the individual steps of the modulation anddemodulation processes inside the blocks representing demodulator 431 aand modulator 432 a.) Coupler 433 recombines the signals, which areexpressed within non-overlapping frequency bands, providing them tofilter 460 along the same conductive path.

Import processor 440 c (shown at the bottom of FIG. 11b), is designed toblock convert signals from one frequency range to a second frequencyrange. Referring to FIG. 8, assume that in addition to video signal Vtransmitting between 1 and 6 Mhz, a second video signal (not shown inFIG. 8) is amplitude modulated between 6-12 Mhz and transmits acrossextended pair 405 b. Both these signals transmit to import processor 440c and are upshifted in block converter 434 by 60 Mhz, thereby convertingthem to frequency bands of 61 MHz-66 MHz (VHF channel 3) and 66 MHz-72MHz (VHF channel 4), respectively. Because these channels are tunable byordinary televisions, video receiver 419 b will not need to convert thesignals before transmitting them to television 492 b. The signals areamplified after conversion, then exit towards filter 460 and are appliedto local network 411 b. This block conversion can also enable the videosignals to coordinate (i.e., avoid interference) with video signalstransmitting locally across local network 411 b, i.e., between videotransmitter 417 b and video receiver 419 b.

Import processor 440 c includes sloped amplifier 498 and block converter434. Sloped amplifier 498 performs a process similar to that of importprocessor 440 a. It amplifies the input, but imparts more gain to thehigher frequencies because they have attenuated more during transmissionacross the associated one of extended pairs 405. The output of slopedamplifier 498 is fed to block converter 434. As is seen in FIG. 11b,that component shifts the signal in frequency by an amount equal to thefrequency of a local oscillator. In the example above, the shift is 60Mhz. The resulting signal is passed through a filter, amplified, andtransmitted to filter 460. (In the example above, filter 460 would passonly the frequencies between 60-72 Mhz.) To allow import processor 440 cto be used in a variety of installations, the gain of the amplifier inblock converter 434 is manually adjustable, as is the slope of amplifier498. (In practice, these settings would be adjusted to provide all ofthe output signals at levels that generate radiation slightly below thegovernmental limit.)

Export processor 441 receives signals from local network 411 b andconverts them to the waveform, frequency, and signal level at which theyare fed, ultimately, to extended pair 405 b. Two embodiments of exportprocessor 441 are shown in FIG. 11c, and are now described.

Export processor 441 a amplifies the level of the signal applied to it,providing these signals on output at levels that will create radiationon the extended pair 405 just below the legal limits. As such, it mustimpart a higher gain to the higher frequency signals because they havesuffered more attenuation in transmitting across network 411 b. Thus, itworks in a manner identical to import processor 440 a (FIG. 11b), andits components, amplifier 499′ and sloped filter 497′, correspond infunction to amplifier 499 and sloped filter 497 of processor 440 a.

Export processor 441 b is designed to provide frequency and/or waveformconversion for one of its input signals, and to simply adjust the energylevel of the others. The signals received by export processor 441 b passto splitter 484, which directs the signals to both demodulator 457 andfilter 482. Demodulator 457 selects one of the signals for demodulation.The basebanded result is passed to modulator 456 which remodulates thesignal, providing it with a different waveform, frequency, and energylevel. (The typical modulation and demodulation steps are shown internalto the blocks representing modulator 457 and demodulator 456.) Filter482, meanwhile, filters out the signal selected by demodulator 457,passing the remaining signal or signals for amplitude adjustment by gaincontrol 481 to a fixed level, typically resulting in a level increase.(Gain control 481 performs its processing in a manner identical to theprocessing performed by export processor 441 a and import processor 440a.) The output of gain control 481 and the output of modulator 456(which are in different frequency bands) are then combined onto the sameconductive path by coupler 465, and passed to filter 445.

Referring to FIG. 8, an example of the processing conducted by exportprocessor 441 b is given. Video receiver 419 b provides control signal Bbetween 22.75-23.25 Mhz and feeds it onto local network 411 b, and videotransmitter 417 b feeds video signal W onto local network 411 b, usingamplitude modulation between 6-12 Mhz. At local network interface 404 b,video signal W is selected and demodulated by demodulator 457, and thenfrequency modulated between 24-54 Mhz by modulator 456. Control signalB, meanwhile, passes through filter 482 to gain control 481, whichincreases its energy level. These two signals are then joined by coupler465 and fed onto extended pair 405 b by other components of localnetwork interface 404 b.

5) An Embodiment of Local Processor 439 that Retransmits SignalsRecovered from Local Network 411 b (FIG. 12)

As discussed above, FIG. 10 shows a general embodiment of processor 439.As can be seen from that figure, processor 439 receives signals fromlocal network 411 b and also transmits signals onto that network. (Thesignals transmitted onto local network 411 b are either received fromextended pair 405 b, received from local network 411 b, or they aregenerated internally.) In the more specific embodiments shown in FIGS.11a-11 c, only those signals recovered from extended pair 405 b are fedonto local network 411 b.

Processor 439 b, shown in FIG. 12, is a different specific embodiment ofprocessor 439, and is described in this section. In contrast toprocessor 439 a, the signals transmitted onto local network 411 b byprocessor 439 b can come from two sources: 1) they can be signalsrecovered from extended pair 405 b, or 2) they can be signals receivedfrom local network 411 b.

There are several reasons to provide for both sources. One of theadvantages is that it allows for certain simplifications and economiesin design of the components that receive the video signals, i.e., videoreceivers 419. It also allows for modifications of the retransmittedsignals to be applied by a single device, i.e., the device performingsuch retransmission. Such modifications can include superposition oftextual information such as a clock, a channel display, etc.

These advantages are described in the second CIP application, wherein asimilar signal processing device, RF video processor 312, is described.That device recovers video signals from a network of telephone wiring,processes those signals, and retransmits them onto the same network.Processor 312 is slightly modified in this application to provideprocessor 439 b. More precisely, RF/video processor 312, shown in FIG. 2of the second CIP application, is modified and combined with mastercontroller 316 of the second CIP application to provide a specificembodiment of the following elements of this application: processor 439,filters 461, 460, 463, and coupling network 449.

To see how RF/video processor 312 is modified, realize that two of thefunctions of processor 439, receiving signals from network 411 b andtransmitting them onto that network, are already part of processor 312.The other two functions, receiving signals from extended pair 405 b andconverting signals and feeding them through filter 445 and onto extendedpair 405 b, are provided in the following manner.

As described in the second CIP application, signals output fromgraphical processors 329 are basebanded video signals, but they can alsobe basebanded signals of a general nature. Any one of these outputs canbe split, under control of master controller 316, and fed to processor473. Processor 473 converts the signal to the waveform, frequency, andamplitude at which it will transmit across extended pair 405 b. Finally,the signal is fed through port 321 to filter 445. After passing throughthat filter, the signal follows the transmission path, described above,onto extended pair 405 b.

As described earlier, signals received from extended pair 405 b passthrough filter 438. To feed these signals to processor 312, a conductivepath is provided between filter 438 and port 315. (In the second CIPapplication, one intended function for port 315 was to input cable TVsignals.) Thus, this simple connection, plus processor 473, are the onlyadditions necessary to adapt processor 312 to perform all of thefunctions of processor 439.

Note that in the embodiment shown in FIG. 12, filter 461 is actually twoseparate filters, as is filter 460. Furthermore, each conductive pathleading to and from those filters is actually composed of two separateparallel paths. This separation is due to the fact that in thisembodiment, processor 439 recognizes a separate class of signals andprocesses them differently.

The signals in the special class are those intended communicate withmaster controller 316, and also signals sent by controller 316 that areintended to control devices that receive signals from or transmit themto local network 411 b. In particular, the control signal from infraredtransmitters 493 b are detected by video receiver 419 b, converted tovoltage, and fed onto network 411 b. This signal passes through filter334 to processor 330.

In the reverse direction, master controller 316 instructs control signalcreation circuitry 338 to generate control signals and feed them throughfilter 336 (part of filter 460) onto local network 411 b. These signalswill be received by video transmitters 417 and converted to infraredsignals that are broadcast into the environment where they can bedetected by nearby infrared responsive devices, such as TV 492 b. Thiscommunication process is described more fully in the second CIPapplication.

L. Boosting Signal Power within a Wiring Closet (FIG. 14)

As discussed above, the twisted pairs providing telephone service to theunits of an apartment building often converge in a room in the basementof such a building, providing a point of common access to a large numberof units. Other “common points of access” often available in anapartment building are the wiring closets that are often located onevery floor. These provide an intermediate point of convergence to thetelephone wires of the units on that floor. Bundles of multiple twistedpair wires often lead from the basement location to the wiring closets.

Locating transceiver/switch 400 in the basement is an economicalalternative because it frees one from the requirement of bringingcommunication line 402 to the wiring closet of each floor, and becauseone device embodying transceiver/switch 400 can suffice for the entirebuilding. (Although this device will need to have more internalcomponents, economies will be enjoyed in hardware, maintenance, andinstallation.)

In very large apartment buildings, however, the distances may be suchthat extended pairs 405 will be relatively long for certain apartmentunits. As is described above, this increases the attenuation oftransmission, preventing the use of higher frequencies and limiting thenumber of signals that can transmit at a single time. One solution tothis problem is to provide amplification of the signals at anintermediate points, such as in the wiring closets.

Amplification at an intermediate point is most useful if half of thesignal attenuation occurs before amplification, and half occursafterwards. It can be shown that this maximizes the SNR at the receiveend. To see this, assume that amplifying a particular signal to 50 dBand applying it to telephone wiring creates EMF radiation just below thelegal limits. Assume further that a given transmission path imparts 30dB of attenuation and that the noise level at the input to the amplifierand at the input to the receiver at the end of the path is 5 dB mV.Assuming the signal encounters the amplifier after 25 dB of attenuation,the SNR at the amplifier input will be 20 dB. Because the amplifierprocesses signal and noise in parallel, and both signal and noiseattenuate in parallel during transmission to the receiver, the SNR willbe no higher than 20 dB at the input to the receiver.

Now assume that the amplifier is encountered after only 5 dB ofattenuation. The signal level at the amplifier output will still be 50dB mV but 25 dB of attenuation is encountered in transmission to thereceiver, making the signal level 25 dB mV at that point. Because thenoise will again be at its 5 dB mV minimum, the SNR will be 20 dB.

By contrast, if amplification is applied after 15 dB of attenuation,which is the “midpoint”, the signal level at both the amplifier inputand the receiver input will be 35 dB mV, and the SNR at the receiverwill be 30 dB.

Often, signal loss is divided approximately evenly between theattenuation of transmission on extended pairs 405, and the attenuationcause by the splits in signal energy that occur at the junctions oflocal networks 411. This is an important reason why local networkinterfaces 404 are useful. When transceiver/switch 400 is located on atelephone pole, for example, the initial signal level is oftensufficient to provide a good SNR at each of local network interfaces404, and the received signal is then boosted to transmit across localnetworks 411 to present at a receiver 419 with adequate SNR.

The wiring configuration of most apartment buildings offers a similaropportunity. Specifically, amplification devices can be placed in thewiring closets to boost the level of the signals transmitting in bothdirections between transceiver/switch 400 and local networks 411. Assuch, this booster serves the function of local network interfaces 404,being located in a wiring closet instead of being mounted on the anexternal wall of a house.

A major advantage of this location is that one electronic device canprovide the hardware for several local networks 411 at the same time.This provides hardware, installation, and maintenance economies. (Adisadvantage is that the wires from several local networks 411 are stillclose enough to make crosstalk an issue.)

FIG. 14 shows a design for wiring closet booster 504, which houses localnetwork interfaces 404 a, 404 b, and 404 c. A situation where localinterfaces 404 a-404 c can be co-located can occur, for example, whenthe five local networks 411 are located in different units in anapartment building, and the units of local networks 411 a, 411 b, and411 c are located on the same floor and served by the same wiringcloset.

Only the details of local network interface 404 b are shown.Furthermore, it is seen that the signal processing in each of 404 a, 404b, and 404 c is independent and that they operate on different signals.It will be appreciated, however, that local interfaces 404 a-404 c canbe serviced by the same power supply. This is one of the hardwareeconomies of including them in the same housing.

The embodiment of local network interface 404 b shown in FIG. 14 issimilar to that shown in FIG. 10. The only differences are that some ofthe components are replaced by components that represent more specificembodiments. Specifically, coupling network 437 a, telephone signalprocessing section 470 a, and local processor 439 a, represent couplingnetwork 437, telephone signal processing section 470, and localprocessor 439. Internal to local processor 439 a, import processor 440 arepresents import processor 440, and export processor 441 a representsexport processor 441.

According to the descriptions, provided above, of the components thatare shown in FIG. 14, telephone signals transmit at baseband throughtelephone signal processing section 470 a between extended pair 405 band network 411 b. Also, non-telephone RF signals fromtransceiver/switch 400 transmit through coupling network 437 a, filter438, import processor 440 a, filter 460, coupling network 449, andfilter 463 onto local network 411 b. In the opposite direction,non-telephone RF signals transmit from local network 411 b throughfilter 463, coupling network 449, filter 461, export processor 441 a,filter 445, coupling network 437 a and across extended pair 405 b totransceiver/switch 400. Filters 460 and 445 are shown with dashed linesbecause these filters may not be necessary if the directionalmultiplexing in coupling networks 437 a and 449 provides strongisolation of transmission paths.

Important to booster 504 are import processor 440 a and export processor441 a. These components amplify their input signals, outputting theindividual signals in the various frequency bands at the energy level atwhich the radiated energy they create is just below the legal limit.This maximizes the SNR of non-telephone signals received from localnetworks 411 a-411 c, and the SNR of non-telephone signals received fromtransceiver/switch 400.

There may be applications for allowing for communication between localnetworks 411 by transmitting signals between the ones of local networkinterfaces 404 located together within wiring closet booster 504. Thisfunction is contemplated within this disclosure but technology toachieve it is not specifically described.

M. Transmission of Compressed Digital Video Signals (FIG. 15)

As described above, NTSC video signals can be digitized and compressed,without losing information content, so that the resultant digitalbitstream has a data rate that is slow enough to be expressed as ananalog waveform in a remarkably narrow channel. Specifically, theresulting waveform can be confined within channels less than 4 Mhz wide,and can be accurately received with SNRs less than 30 dB. Thus, videosignals encoded in this manner are more amenable to transmission withinthe system disclosed herein than even FM video signals.

Transmission of digital signals between transceiver/switch 400 and localnetworks 411 was described above. Conceptually, these components aresufficient to transmit a digital bitstream representing a video signal.That description, however, does not include the digitization andcompression components that may be used to convert the signal at thetransmit end, and does not include the elements that may be used toreconstruct the signal so that it can be viewed at the receive end.Those components and the manner in which they coordinate with the otherelements of this communication system are the subject of this section.

As mentioned earlier, electronics that digitize and compress analog NTSCvideo signals in real time are relatively expensive, as are theelectronics that perform the subsequent reconstruction of the analogsignal from the digital bitstream. The expense typically increasesdramatically with the compression ratio, so that a compression processthat allows the resulting bitstream to be expressed in bandwidths lessthan 4 Mhz and minimum SNRs less than 30 dB is relatively complex andcostly.

As a result, transmission of compressed digital video is comparativelyless complex and expensive if the video signals on communication line402 are already in this form (i.e. an analog waveform representing acompressed digital bitstream) when they are applied totransceiver/switch 400. Such a system can be very economical indistribution of cable TV, where a group of video signals is to be madeavailable for selection by a large number of subscribers. The economyarises from the fact that this single group of signals need be digitizedand compressed only once—at the headend of the cable system.

Referring to FIG. 5a, signal distribution subsystem 403 a can selectdigitized video signals from communication line 402 and to feed themonto extended pairs 405. Indeed, transmission of these signals is, as apractical matter, no different than transmission of the digital signalsdescribed above.

Following is an example. Assume communication line 402 is a singlecoaxial cable that provides 60 channels of digital video signals,confined within adjacent 4 Mhz bands that extend between 200 Mhz and 440Mhz. These signals are received by interface 409 and transmitteddirectly to splitter 426′ in subsystem 403 a. (I.e., interface 409 doesnot block shift or otherwise process these signals.) Splitter 426′ feedsthe signals to each demodulator 426. Under control of master controller415, demodulator 426 a basebands the channel between 204 MHz and 208Mhz, and transmits it to switch 462 a, which in turn applies thisbasebanded signal to modulator 410 d. Modulator 410 d remodulates thesignal, using AM, to the frequencies between 12 MHz-16 Mhz. Thus, theeffect of this modulation/demodulation is simply to shift the signal tothe new band. The output of modulator 410 d is fed to switch 401, andthat device directs the signal through signal separator 413 b ontoextended pair 405 b.

If subsystem 403 c (FIG. 5c) is provided instead of subsystem 403 a, theprocessing and signal flow work similarly. In this case, RF processors485 convert the selected signal to the channel between 12 MHz and 16Mhz.

If local network interfaces 404 are provided, they can receive thedigital signals from extended pairs 405, amplify them, convert them infrequency, and retransmit them onto local networks 411, all using thetechniques described above. If local network interfaces 404 are notprovided, these are signals transmitted directly onto local networks 411confined within a channel whose bandwidth is the same as the originalchannel confining the digital signal.

Referring to FIG. 15, the digital signals transmitted onto localnetworks 411 are received by digital video receiver 505. This device isnot shown connected to any local network in FIGS. 1a or 1 b. It is shownconnected to TV 492 b and local network 411 b, however, and itcoordinates with the rest of the system components in the same manner asvideo receiver 419 b.

In a general sense, this receiver is identical to television transceiver15, shown in FIG. 2 in the parent application. Specifically, videoprocessing circuitry 506 corresponds to RF converter 19, couplingnetwork 513 corresponds to coupling network 18, and control signalprocessing circuitry 514 corresponds to control signal processingcircuitry 17.

Video signals from local network 411 b are blocked from telephone device414 b by the low pass filter and are directed by coupling network 513 tovideo processing circuitry 506. Coupling network 513 and circuitry 514function identically to their corresponding components in transceiver15.

Like RF converter 19, video processing circuitry 506 converts thereceived video signal to a form that is tunable by ordinary televisions.The following process is used, however, because the signal is an analogrepresentation of a bitstream that represents a video signal.

In the first stage of the processing, the video signal is basebanded inthe ordinary fashion. The elements in FIG. 15 show the steps of thisprocess: shifting to an intermediate channel by mixing with a localoscillator, filtering of the intermediate channel, and thendemodulation. Using the example above, the 16 MHz-20 Mhz signal may beshifted to the 40 MHz-44 Mhz band, filtered, and then detected,resulting in a basebanded signal. Alternatively, the “intermediatechannel” can be fixed at 16 MHz-20 Mhz, removing the need for frequencyshifting.

In the second stage, the basebanded analog signal is converted to adigital bitstream, which is decompressed in real time. In the classicprocedure, a digital process reads the bitstream and uses that data tofill out a matrix of storage locations representing the pixels of theimage. This matrix is refreshed 60 times a second, the “refresh rate” ofNTSC video. The actual NTSC signal is then created by scanning acrossthe storage locations (conceptually, the pixels of a frame) just as avideo camera creates a picture by scanning across a photoconductivegrid.

The third stage is the modulation stage. The newly recreated NTSC signalis passed to this stage at baseband. It is mixed using a localoscillator, creating an AM NTSC signal in the ordinary manner. Thissignal is passed to TV 492 b.

Note that channel selection still takes place in the ordinary manner.Using the examples above, IR transmitter 493 b issues infrared signalsthat are detected by the IR sensitive diode of receiver 505. Thesesignals are converted by circuitry 514 to, for example, a 0.5 Mhz signalcentered at 23 Mhz. (This is the frequency used for communication ofcontrol signals in FIG. 8.) These signals are applied to local network411 b and transmit to master controller 415 using the circuitry andsignals paths described in the sections above. In response to thissignal, controller 415 can instruct demodulator 426 a to select adifferent channel from among the 60 available between 200 MHz-440 Mhz oncommunication line 402.

When FM communication techniques are not sufficient due to the length ofextended pairs 404 and the nature of local networks 411, communicationof the video signals in compressed digital form is indicated, even ifsignals are provided by communication line 402 in analog form. In thatevent, digitization and compression are performed prior to transmissiononto extended pairs 405. This conversion can take place in signaldistribution subsystem 403 a.

Referring to FIG. 5a, the desired result can be achieved by replacingone of modulators 410 for every digital video signal provided byprocessor 418. The new processors 410 are similar in that they receive abasebanded video signal and output an analog waveform confined within aparticular channel at a signal level that creates radio energy justbelow the legal limits. The difference is that the waveform nowrepresents a compressed digital bitstream, which in turn represents theoriginal NTSC signal.

The above description includes the components used to transmit digitalvideo signals from transceiver/switch 400 to local networks 411. Similartechniques can be used for transmission in the opposite direction butare not specifically described herein.

N. Transmission of Video Signals Across Computer Communication Networkswith “Star” Configurations (FIG. 16)

As described in the summary section, in many office buildings, thetelephone wiring is not the only network of twisted pair wiring thatextends to each office and converges at a common point. Over the pastseveral years, common communication networks that connect personalcomputers, known as Local Area Networks or LANs, have begun to usetwisted pair wiring for their conductive paths. In the typicalconfiguration, a digital electronic device serves as the “hub” for sucha system, and a separate twisted pair wire connects from the hub to eachof the computer nodes in a “star configuration”. In this section, thetechniques described for communication across wiring networks thatconduct telephone communication are extended to provide the samecommunication capabilities across computer networks that used twistedpair wiring and adopt such a “star” configuration.

To illustrate such a star configuration, one need only change a few ofthe elements of the setup shown in FIG. 1b. The result is shown in FIG.16. One change is that PBX 500 is replaced by communications hub 519,which is the digital device that serves as the “nerve center” of thecommunication system. Another change is that line 475′ is not required.Finally, telephone devices 514 are replaced by computers 518, which arethe devices that communicate across the network using the conceptsdescribed herein.

The only fundamental change required when the communication medium isprovided by this new system is that the lower bound on the frequenciesavailable for communication with line 402 (or for communication betweenthe RF transmitters, receivers, and transceivers connected to the localnetworks) will be higher. Specifically, the lower bound must be abovethe highest frequency used for communication between computers 518 andhub 519. For example, when the computer communication system follows the10 Base T standard, which is the most popular standard for local areanetworks that use twisted pair wires, the computers communicate atfrequencies up to 15 Mhz, and the lower bound must be above that abovethat frequency.

Following are the electronic changes that should be made to provide allof the functions discussed above:

1) The low pass filters connecting between computers 518 and local areanetworks 511 must have higher cutoff values. Specifically, the cutofffrequency must be high enough to pass the communication signalstransmitting between hub 519 and computers 518.

2) The cutoff frequency of low pass filters 474 (FIG. 2) is increased ina similar fashion. The cutoff frequency of low pass filter 442 shouldalso be increased if local network interfaces 404 are provided.

3) The cutoff frequency of hi-pass filter 451, which is part of signalseparators 413 shown in FIG. 9a, should be raised above the highestfrequency used by computers 518. Thus, this filter will not pass some ofthe lower frequency signals it passed previously.

4) The spectral distributions shown in FIG. 3 will not be available ifthey overlap the frequencies used by the computer signals. Higherfrequencies can be used.

5) The minimum frequencies suggested in Section C will also not beavailable if they overlap the frequencies used by the computer signals.

O. Preventing Unintended Reception and Control Signal Confusion

The problem of energy from one extended pair crossing over to a secondpair and causing interference with video signals was described above.One proposed solution was to lower the susceptibility to interference byencoding the signals using frequency modulation. Susceptibility would bereduced because of the low “capture ratios” exhibited by FM receivers.

A second problem is caused by energy crossover, however, that may not beadequately addressed by low “capture ratios.” This problem is one thatarises when the second pair is not being used to conduct video signals,and the energy crossing onto that wire is sufficient to allow receptionof the signal on the local network to which the second extended pairconnects. A related problem is where the control signal transmitted ontoone extended pair crosses over to a second pair, causingtransceiver/switch 400 to react as if a control signal had genuinelybeen applied to the second pair.

The proposed solution is to ensure that a signal always transmits ontoeach of the extended pairs in a bundle within each of the channels usedfor transmission, whether or not a genuine signal is intended forconduction at that channel. A convenient way of doing this is totransmit the unmodulated carrier for every channel onto those wire pairsthat are not intended to conduct a signal at that channel. Similarly,continuously transmitting the carrier of the control signal can solvethe related problem of control signal “confusion.”

Following is an example using the signals listed in FIG. 8. Note thatvideo signal V is transmitted onto extended pair 405 a between thefrequencies of 7 Mhz and 22 Mhz. This signal is created by frequencymodulating a carrier of 14.5 Mhz, and is received by local networkinterface 404 a and relayed onto network 411 a. Assuming that signal Vwas not transmitted onto extended pairs 405 b and 405 c but crosses overonto pairs 405 b and 405 c, there would be a danger that the crossoversignal V could be received by local network interfaces 404 b and 404 c.(FIG. 8 shows that signal V is indeed transmitted to networks 411 b and411 c between 1-6 Mhz, but we will ignore that fact for the purposes ofthis example.) The proposed solution is to transmit the unmodulated 14.5Mhz carrier onto extended pairs 405 b and 405 c, lowering the SNR of thecrossover video signal V received by local network interfaces 404 b and404 c below acceptable levels.

Continuing the example, users at network 411 a may issue infraredcontrol signals that are transmitted over extended pair 405 a bymodulating a carrier with a fundamental frequency of 23 Mhz.Theoretically, these signals can crossover onto extended pairs 405 b and405 c, incorrectly exciting control signal processor 420 intransceiver/switch 400. The proposed solution is to have video receivers419 b and 419 c continuously feed their 23 Mhz carrier, unmodulated,onto networks 411 b and 411 c (from which they are relayed onto extendedpairs 405 b and 405 c by local network interfaces 404 b and 404 c.)

Still other embodiments are within the scope of the following claims.

What is claimed is:
 1. A method for communicating information between anexternal source of information and a plurality of destinations ofinformation over a telephone wiring network used for passing telephonesignals in a telephone voice band between a plurality of telephonedevices and a telephone exchange, comprising: receiving at a signalinterface a plurality of external data streams from the external sourceof information; Manchester encoding the external information streams toproduce Manchester encoded signals with signaling rates such that theenergy of the encoded signals is concentrated primarily at frequenciesabove the telephone voice band; and transmitting the Manchester encodedsignals over the telephone wiring network to each transceiver.
 2. Asystem for communicating information between an external source ofinformation and a plurality of destinations of information over atelephone wiring network used for passing telephone signals in atelephone voice band between a plurality of telephone devices and atelephone exchange, comprising: a plurality of transceivers coupledbetween the telephone wiring network and corresponding destinations ofinformation, each including circuitry for accepting signals in a highfrequency band of frequencies above the highest frequency of thetelephone voice band and rejecting signals in the telephone voice band;and a signal interface coupled between the external source ofinformation and the telephone wiring network, including circuitry forreceiving a plurality of data streams from the external source ofinformation, circuitry for Manchester encoding the received data streamsto produce Manchester encoded signals with signaling rates such that theenergy of said signals is concentrated above the telephone voice band,and circuitry for transmitting the Manchester encoded signals over thetelephone wiring network to each transceiver.
 3. The system of claim 1wherein the Manchester encoded signals are Ethernet 10Base-T signals.